Purchased 87 chevy scottsdale approx 3 months ago for son and ranch truck. Its in excellent condition with 117,ooo original miles, 5.o liter with auto trans, 4wd, Throttle body injection with dual tanks. Runs great and strong. My problem is when you drive it for extended period of time, sometimes 45 to an hour, it starts to run like crap. Its starts to idel rough and loose power upon acceleration. As you drive it more, it gets worse, just sound like its not getting enough fuel, its pings and back fires and bogs down. Mechanic has had it 4 times now. First ran all diagnostics, checked fuel filter, stated no problems, no code on computer. Had 3 days, could not duplicate problem. Got truck back, drove it around and it started to happen again, only after extended driving. Took back to mechanic, told me to replace control module in distributer possible bad module when it gets warm, did it, did not resolve problem. Took back again, replaced distributer thinking pick up coil. checked fuel pressure, stated 16 psi. (All of this time Ive has a friend, who is a custom engine builder and former dealership mechanic,tell me to replace fuel pump, but mechanic said it was not pump, more likely ignition) New distributer, left me on side of road 3 time on sunday. Drove 45 minutes to ranch, started to run rough again, barely made it home, no power, sounded as if it was leaning out. Called back and told him to replace fuel pump, charged me $200.. parts and labor. Have not driven yet. I will this weekend and see what happens. If it happens again, any GM tech here that knows what else it could be?? Its really starting to bother me. Any common issues 87 trucks with TBI that anyone can recall? I have been told by another friend, mechanic, that it could be the fule pressure regulator, oil sending unit that runs the fuel pump??? MAP sensor??? I am trying to avoid bring to local chvy dealership, just because of labor cost, but I ned this to be reliable. The thing that kills me is it runs great until a certain point. If i leave it sit overnight, its fine.