I have a 1995 Pontiac Grand SE v6. When I’m driving my car, as soon I come to the stop, my car tries to die. And when I get over 55 mph, my engine light comes on, but the car still drives fine.
The first step is to have the car’s OBD system scanned for trouble codes.
The presence of an illuminated Check Engine Light means that there should be a trouble code stored by the system.
Many auto parts stores will do this for you without charging a fee, but since your car uses either an OBD1 or an OBD 1.5 system rather than the more modern OBD 2 system, not many parts stores will have the appropriate code reader. I suggest that you call a few parts stores in your area to see which one(s) might be able to help you.
Put the car into neutral just before you come to a stop to see if it runs normal after stopping. If so put it back into drive. If it dies then suspect the transmission torque convertor clutch. It may be locking up and not releasing. Fix may be a solenoid in the trans pan attached to the valve body.