1991 cutlass calais

i have a cutlass calais that i want 2 last until i go 2 recruit traning for the marines in march of 08'. with like 139,000.it has a 2.3l quad4 HO. it runs fine in the city. but when i take it on the highway(i have 2 to get 2 work) then get off and stop at lights or stop signs it stalls. i think its overheating but my fluid is right at the line its suppposed to be and ive tried driving with my heater on full blast. if i just drive around the city like going less than 45ish it wont stall just after i get off the highway any suggestions????
please and thank youu

Welcome to AF. If this stalls slowing down, shaking as it does, then when you put it in neutral it starts right back up, but stalls when put in gear, this is the trans TCC solenoid. Very common problem on that trans.

thanks. but my car is an automatic does that make a difference??

No. the torque converter clutch is supposed to unlock when you hit the brakes so it doesn't stall out the engine. if the solenoid is bad it won't release the tcc which would cause the engine to stall in drive. the transmission doesn't shift into overdrive at speeds lower than 45 which is why it is fine in the city.