Below are but a few documentation references from Mormonism sources showing this heresy:
Those who gain exaltation, having thus enjoyed the fullness of eternal progression, become like God. It should be realized that God is not progressing in knowledge, truth, virtue, wisdom, or any of the attributes of godliness. He has already gained these things in their fullness. But he is progressing in the sense that his creations increase, his dominions expand, his spirit offspring multiply, and more kingdoms are added to his domains. (Doctrines of Salvation, vol. 1, pp. 5-10.)"We were begotten by our Father in Heaven; the person of our Father in Heaven was begotten on a previous heavenly world by His Father; and again, He was begotten by a still more ancient Father; and so on, from generation to generation, ... we wonder in our minds, how far back the genealogy extends, and how the first world was formed, and the first father was begotten" (Orson Pratt, The Seer, p.132).
"Some people are troubled over the statements of the Prophet Joseph Smith.... The matter that seems such a mystery is the statement that our Father in heaven at one time passed through a life and death and is an exalted man. This is one of the mysteries.... The Prophet taught that our Father had a Father and so on. Is not this a reasonable thought, especially when we remember that the promises are made to us that we may become like him?" (Joseph Fielding Smith, Doctrines of Salvation, vol. 1, pp.10, 12).
In the beginning, the head of the Gods called a council of the Gods; and they came together and concocted a plan to create the world and people it. (Joseph Smith, Journal of Discourses, Vol. 6, p. 5, 1844)
Smith's worldview of time as it pertains to the gods: Smith believed in a "beginning" that was operative before the Mormon plan to the create this world. The question becomes, who is the head of the Gods as pertains to this council of gods?
In the very beginning the Bible shows there is a plurality of Gods beyond the power of refutation. It is a great subject I am dwelling on. The word Eloheim ought to be in the plural all the way through--Gods. The heads of the Gods appointed ONE God for us... (Joseph Smith, Teachings of the Prophet Joseph Smith, p. 372)
When God makes us a promise that if we do X he will bless us with Y, we believe it. That doesn’t mean we don’t recognize that Y is far in excess of what we deserve, even when we’ve done X.