bronco II 89 aut. transm probs

Hi i just bought a bronco II 89 aut. and 2 days later i am having problems with the transmission, it seems like its stuck on over drive. it wont shift between 0-80... sometimes unless i push the gas hard...
could it be the computer or the transm?
help!!!!!!!!

First off check the fluid level, is the fluid old and dirty looking, does it smell burnt. The way you discribe it, it sounds like a low fluid problem. If it low, I would suggest a transmission flush. You should be able to find a garage that has a transfussion machine. It does cost a little but it is worth it.