1988 Chevy Cheyenne Stalls when a Load is put on the engine

The truck idled rough but drove when I got it. After it sat for a few months while repairing the body it would stall out when you dropped it in gear, we put a tps, iac, map, coolant temperature sensor and an egr on it, checked the fuel pressure and it was fine. We also checked for vaccum leaks and checked the intake manifold gasket and no leaks were found. Now it goes on a flat surface about 25, but when you try to accelerate on the flat or a hill it bogs down and you have to feather the gas to keep it alive, I am at a loss and have run out of ideas of what it could be.