i have a 1991 gmc pick up 1500 4x4 auto trans 5.7l. come to a stop light and the truck cut off started back up put it in gear and it cut back off then would not start. tried the next morning it started up and ran for a couple minutes then started blowing black smoke and cut off and would not start. was tuned up several months ago. when it wont start it turns over good it has spark you can smell fuel and you can see fuel shooting into the carb.unhooked the exhaust still wont start.has service eng. soon light on has a temp sensor code.
I would start with the black smoke, sounds like a carb float or needle and seat problem.
If in fact the truck has a carburator, that is the problem. The carb needs to be rebuilt and I’d suspect bad floats or needle valves are at the root of the problem.