you can only transfer after M2 (when everyone is the same because they have all passed step 2), and its still very hard to do. a friend transferred to UTHSCSA and said there were 5 applicants and he was the only one that got accepted.
Well then,if i were the OP, i would pick one and make the best out of it. I've come to the conclusion that all texas schools are good. if u don't get into #1, u can still be happy at #4. Four years goes by very fast. u'll be out soon enough.