Well, there wasn't much reason to check with anyone. It was just a d*mn piece of luggage in the back seat. I will complain, but I doubt if I will do a "formal" complaint.
Texas plates used to be more or less county specific, but not any longer.
If you are going to complain, go the whole hog. File it.
I thought in TX a unmarket car can NOT pull someone over for speeding. Maybe that is why he said you were "weaving" all over the road instead of speeding like most traffic stops on the highway.