1995 lesabre wheezing and racing

car runs perfect for an hour or so, then when outside temp goes up, or after very heavy load (like driving from denver to the eisenhower tunnel)it will all of a sudden start wheezing like an asthmatic. and yes, the air filter is fine. the tach races up to about 2500 rpm, then slows to arount 900 rpm. about 3-5 seconds for each cycle of this. power declines rapidly until you have to pull over. after you sit with engine off for 15 minutes or so it will start up and run JUST FINE until this starts up again.

at first i could avoid this by running in third gear instead of overdrive, but now that is not doing it. a shop told me it was the tranny and would need to be replaced, which is about enough to junk this car. the last time i had it doing this i pulled over and put it in neutral before it shut off, and it still shut off. does this mean it may not be the transmission? anyone have this kind of problem with the GM 3.8? tranny fluid looks good. no sounds noticed from the tranny.

computer chip? sensor?

the car runs smooth as silk until this starts up out of the blue.