Can someone help me understand what appears to be a contradiction?

I'll try, but I'm not a biblical scholar.

Part of it might well be your translation.

Matthew 3: 13-15

"Later Jesus, coming from Galilee, appeared before John at the Jordan to be baptized by him. John tried to refuse him with the protest, "I should be baptized by you, yet you come to me!" Jesus answered: "Give in for now. We must do this if we would fulfill all of God's demands." So John gave in."

Matthew 11: 2-6

"Now John in prison heard about the works Christ was performing, and sent a message by his disciples to ask him, "Are you, 'He who is to come" or do we look for another?" In reply, Jesus said to them: "Go back and report to John what you hear and see: the blind recover their sight, cripples walk, lepers are cured, the deaf hear, dead men are raised to life, and the poor have the good news preached to them. Blest is the man who finds no stumbling block in me."

Is the contradiction you perceive in the the two questions and that John was sure and then he wasn't? In Matthew 11, the next paragraph seemed to explain the fulfillment of the prophecy.

Maybe it was a device used to explain and prove that Christ was the messiah...

Others will probably have better explainations, but a different translation might help you.

Nope. I'd say that the 2nd event has John in prison and he knows that he's going to be killed .... that he'll not get out alive. I think the human side of him was reacting the same way as the other "Elijah" did. When Elijah got despondent about Jezebel, God arranged for him to be taken home.

John got despondent about ever being released from prison. In order to MAKE SURE that his disciples were clear about who Jesus was he arranged for Jesus once more to confirm it to the followers of John.

Notice that the issue went through JOHN'S DISCIPLES.

Just as an aside question of my own....Shark, are you a believer in Jesus?

There were many expectations of the coming Messiah by the Jews. Some of them were correct, some were not. Jesus rocked the boat a lot because He was not what a lot of people were expecting. What John saw at Jesus' baptism was revealed to Him from God. But no doubt, given some of the things Jesus went on to do and say, John later questioned. Even the greatest figures in the Bible have moments of doubt and question, and John properly addresses them to the source of Truth rather than asking others around him.

If you have the time, read The Jesus I Never Knew by Philip Yancey. Yancey does a good job of giving some perspective to how really radical Jesus' teachings and actions were to the people of that time.

Yes, I am.

I also think the human side of him was getting the best of him. He knew than he had to decrease and Jesus increase, but I'm sure he didn't think he was going to be rotting away in prison. I think he was really doubting.

I wouldn't argue with your interpretation because the information we have is scanty. Sometimes, holy speculation is all we have.

John was human. That says a lot to me.

Here is St. Augustine's answer to your question:

Sermon XVI. [LXVI. Ben.]

On the words of the gospel, Matt. xi. 2, “Now when John heard in the prison the works of the Christ, he sent by his disciples, and said unto him, art thou He that cometh, or look we for another?” etc.
1. The lesson of the Holy Gospel has set before us a question touching John the Baptist. May the Lord assist me to resolve it to you, as He hath resolved it to us. John was commended, as ye have heard, by the testimony of Christ, and in such terms commended, as that there had not risen a greater among those who were born of women. But a greater than he had been born of a Virgin. How much greater? Let the herald himself declare, how great the difference is between himself and his Judge, whose herald he is. For John went before Christ both in his birth and preaching; but it was in obedience that he went before Him; not in preferring himself before Him. For so the whole train [Officium.] of attendants walks before the judge; yet they who walk before, are really after him. How signal a testimony then did John give to Christ? Even to saying that he “was not worthy to loose the latchet of His shoes.” [John i. 27.] And what more? “Of His fulness,” saith he, “have all we received.” [John i. 16.] He confessed that he was but a lamp lighted at His Light, and so he took refuge at His feet, lest venturing on high, he should be extinguished by the wind of pride. So great indeed was he, that he was taken for Christ; and if he had not himself testified that he was not He, the mistakewould have continued, and he would have been, reputed to be the Christ. What striking humility! Honour was proffered him by the people, and he himself refused it. Men were at fault in his greatness, and he humbled himself. He had no wish to increase by the words of men, seeing he had comprehended the Word of God.
2. This then did John say concerning Christ. And what said Christ of John? We have just now heard. “He began to say to the multitudes concerning John, What went ye out into the wilderness to see? A reed shaken with the wind?” [Matt. xi. 7.] Surely not; for John was not“blown about by every wind of doctrine.” [Eph. iv. 14.] “But what went ye out for to see? A man clothed in soft raiment?” [Matt. xi. 8.] No, for John was clothed in rough apparel; he had his raiment of camel’s hair, not of down. “But what went ye out for to see? A Prophet? yea, and more than a Prophet.” [Matt. xi. 9.] Why “more than a Prophet”? The Prophets foretold that the Lord would come, whom they desired to see, and saw not; but to him was vouchsafed what they sought. John saw the Lord; he saw Him, pointed his finger toward Him, and said, “Behold the Lamb of God, who taketh away the sins of the world;” [John i. 29.] behold, here He is. Now had He come and was not acknowledged; and so a mistake was made also as to John himself. Behold then here is He whom the Patriarchs desired to see, whom the Prophets foretold, whom the Law prefigured. “Behold the Lamb of God, who taketh away the sins of the world.” And he gave a goodly testimony to the Lord, and the Lord to him. “Among them that are born of women,” saith the Lord, “there hath not risen a greater than John the Baptist: notwithstanding, he that is less in the kingdom of heaven is greater than he;” [Matt. xi. 11.] less in time, but greater in majesty. This He said, meaning Himself to be understood. Now exceedingly great among men is John the Baptist, than whom among men Christ alone is greater. It may also [He gives these two interpretations of this passage; again Cont. adv. leg. and Prop. ii. 5 (20).] be thus stated and explained, “Among them that are born of women there hath not risen a greater than John the Baptist: notwithstanding, he that is the least in the kingdom of heaven is greater than he.” Not in the sense that I have before explained it. “Notwithstanding, he that is the least in the kingdom of heaven is greater than he;” the kingdom of heaven he meant where the Angels are; he then that is the least among the Angels, is greater than John. Thus He set forth to us the excellence [Commendavit.] of that kingdom which we should long for; set before us a city, of which we should desire to be citizens. What sort of citizens are there? how great are they! Whoso is the least there, is greater than John. Than what John? “Than whom there hath not risen a greater among them that are born of women.”
3. Thus have we heard the true and good record both of John concerning Christ, and of Christ concerning John. What then is the meaning of this; that John sent his disciples to Him when He was shut up in prison, on the eve of being put to death, and said to them, “Go, say to Him, Art Thou He that should come, or do we look for another?” [Matt. xi. 3. ] Is this then all that praise? That praise is it turned to doubting? What sayest thou, John. To Whom art thou speaking? What sayest thou? Thou speakest to thy Judge, thyself the herald. Thou stretchedst out the finger, and pointedst Him out; thou saidst, “Behold the Lamb of God, behold Him who taketh away the sins of the world.” Thou saidst, “Of His fulness have we all received.” Thou saidst, “I am not worthy to unloose the latchet of His shoes.” And dost thou now say, “Art Thou He that should come, or do we look for another?” Is not this the same Christ? And who art thou? Art thou not His forerunner? Art thou not he of whom it was foretold, “Behold, I send my messenger before Thy face, who shall prepare Thy way before thee?” [Matt. xi. 10.] How dost thou prepare the way, and thou art thyself straying from the way? So then the disciples of John came; and the Lord said to them, “Go, tell John, the blind see, the deaf hear, the lame walk, the lepers are cleansed, the poor have the Gospel preached to them; and blessed is he whosoever shall not be offended in Me.” [Matt. xi. 4–7.] Do not suspect that John was offended in Christ. And yet his words do sound so; “Art Thou He that should come?” Ask my works; “The blind see, the deaf hear, the lame walk, the lepers are cleansed, the dead are raised, the poor have the Gospel preached to them;” and dost thou ask whether I am He? My works, saith He, are My words. “Go, show him again. And as they departed.” Lest haply any one should say, John was good at first, and the Spirit of God forsook him; therefore after their departure, he spake these words; after their departure whom John had sent, Christ commended John. [Matt. xi. 4–7.]
4. What is the meaning then of this obscure question? May that Sun shine upon us, from which that lamp derived its flame. And so the resolution of it is altogether plain. John had separate disciples of his own; not as in separation from Christ, but prepared as a witness to him. For meet it was that such an one should give his testimony to Christ, who was himself also gathering disciples, and who might have been envious of Him, for that he could not see Him. Therefore because John’s disciples highly esteemed their master, they heard from John his record concerning Christ, and marvelled; and as he was about to die, it was his wish that they should be confirmed by him. For no doubt they were saying among themselves; Such great things doth he say of Him, but none such of himself. “Go then, ask Him;” not because I doubt, but that ye may be instructed. “Go, ask Him,” hear from Himself what I am in the habit of telling you; ye have heard the herald, be confirmed by the Judge. “Go, ask Him, Art Thou He that should come, or do we look for another?” They went accordingly and asked; not for John’s sake, but for their own. And for their sakes did Christ say, “The blind see, the lame walk, the deaf hear, the lepers are cleansed, the dead are raised, the poor have the Gospel preached to them.” Ye see Me, acknowledge Me then; ye see the works, acknowledge the Doer. “And blessed is he whosoever shall not be offended in Me.” But it is of you I speak, not of John. For that we might know that He spake not this of John, as they departed, “He began to speak to the multitudes concerning John;” the True, the Truth Himself, proclaimed his true praises.
Roberts, Alexander and Donaldson, James, Nicene and Post-Nicene Fathers, First Series: Volume VI, (Oak Harbor, WA: Logos Research Systems, Inc.) 1997.