COUGAR

I am looking at a friends car, trying to find out what the hell is going on here. it is a 91 firebird, just the bird. 305 tbi, 700r tans. what is going on is that it shifts alright for the most part, but feels like it is getting confused. when you let off the gas for a minute and then go back on it changes gears right away, like it goes from third to overdrive right away with out any accleration at all. he says it is constant, worse when warm, i drove it, it did it. what is happening, is this a common problem, cuz i don't want it happening to mine if it is. help me out here, or ill be working on this thing all weekend

thanks
COUGAR