1996 GMC Truck distrubance in ignition

After cranked and running, the engine sometimes will just quit. This often is caused by depressing the brake or switching on the lights. At first I thought it to be a fuel problem but I changed the filter, checked for water, and checked the fuel pressure. all were fine. Thinking it may be electrical, I took the alternator and had it checked, it was fine. After it quits, it can be cranked back up but acts as though it has flooded and runs rough. The system is not kicking a code or at least the check engine light has never lit up. Not fully understanding later ignition systems(96 model, I am old) and knowing the expense of replacing these parts, I need advice.

THANKS