1999 GC 4.0 Trans won't come out of 2nd

Over-heated the other day. Since then the trans will not go above 2nd gear. Did I kill it? Or is there some sort of "safe mode" that the trans goes into to protect? If so, How do I reset it?

Please help!!!!!

any error codes? if you don't have an reader, you can take it into auto zone and they'll read the code for free... that's where i'd check first, and i'd be suspecting the transmission control module... same thing happened to me (stuck in 1st gear for me), 'cept i'd shut it down and after i re-started it would shift fine... turned out to be the TCM