Oldsmobile/Buick Repair: car will not idle at stop light-trans remains engaged, cutlass ciera, cruise speeds

Question
I have a 1990 Cutlass Ciera- 160,000 miles-3.3 liter-Plugs, wires  fuel filter replaced at 150,000 miles. The problem is that sometimes after traveling down interstate or just driving for 30 or so miles or minutes when I have to come to an abrupt stop as off an exit ramp or at a traffic light the car will remain engaged in gear and will chug to a stall if I keep the brakes on long enough.(Acts as a manual shift vehicle would act if you did not depress the clutch at a stop.) I used to have no problem with local trips but the problem has become more frequent. Before if I approached stops gently the car would seem to shift down to proper idle position. Car shifts normally up  and down shifts normally if I slow down going up a hill in the neighborhood or if accelerating rapidly down a ramp.I have not had any work done on the transmission in the past.  

Answer
hi mark,well this was one of gm,s not so great idea,s.they deceided with an automatic trans ,even the best they could build ,there is a certain amount of slippage going on at cruiseing spped,causeing lower fuel mileage.so the engineers then deceided that if they could find away to reduce the slippage at cruise speeds this would give them xtra 3 mpg to stay competitive with there competitors. so they put a torque lock switch in this trans and it worked great 55 mph it locks torque converter.almost zero slippage 3 mpg more.but they was not sure what would happen if this part ever failed,well this is what it does.it will not let your trans shift back down in lower gears,so when you stop it is trying to take off in 3rd gear stalling jerking .sound familliar lol.here is what you can do two choices.get the sensor replaced probably 500 dollars. or just simply unplug it .most peoples choice.and you will not lose mileage because it is not working anyway. the plug is located in the front of the trans square 4 or 5 wire plug.this will solve the prob and if you deceide to have it replaced you can at your convienience.good luck please vote for me billymac