Engine is stalling out?

The first thing to look at would be all the secondary ignition components such as dist cap, rotor, wires and plugs. Check out this guide

https://www.2carpros.com/articles/engine-stalls

Please run down this guide and report back.

That doesn't mean they can't have a problem now. You could have cracked a cap at any time or have a damaged plug or wire. It needs to be diagnosed properly to determine what is going on.

You haven't checked anything thoroughly enough to rule anything out. Your going to need some help and test equipment.

Start by checking the fuel pressure.

Rent the gauge from the parts store. Get the gauge hook it up lay the gauge on the wiper arm so you can see the gauge dial. Then close the hood leave the hood on the safety latch. Drive the truck and when it quits read the gauge. Then come back. Gm pumps overheat and stop and than will run ok again till they stop again. Also the hose from the pump to the sending unit gets porce and it sucks air.

When it quits spray the intake with starting fluid. Does it restart?

Gm pumps get hot and stop and go like that. Good luck let us know what happens.

It sounds like you're experiencing a specific issue with your 1991 Chevrolet Silverado during light throttle situations, such as when starting or driving with minimal acceleration. While you've already replaced the spark plugs, cap, rotor, and wires, there could still be other factors contributing to the rough running and stalling. Here are a few additional areas to consider:

Idle Air Control (IAC) Valve: The IAC valve controls the amount of air entering the engine when the throttle is closed. If the IAC valve is dirty or malfunctioning, it can lead to rough idling and stalling during light throttle situations.

Vacuum Leaks: Vacuum leaks can cause poor idling and stalling, especially during specific throttle conditions. Check all vacuum lines, gaskets, and components for leaks or disconnections.

Throttle Position Sensor (TPS): The TPS measures the position of the throttle and sends this information to the engine control module (ECM). A faulty TPS can result in incorrect fuel delivery during light throttle, leading to rough running and stalling.

Fuel Delivery: Check the fuel delivery system, including the fuel filter and fuel pressure regulator. Insufficient fuel pressure could cause issues during light throttle conditions.

Mass Air Flow (MAF) Sensor: The MAF sensor measures the amount of incoming air to adjust fuel delivery. A dirty or faulty MAF sensor can lead to improper fuel-air mixture during specific throttle situations.

Idle Control System: Apart from the IAC valve, other components related to the idle control system could be causing issues. These might include the idle speed control motor or circuit.

Exhaust System: A restricted exhaust system, such as a clogged catalytic converter, can affect engine performance, especially during acceleration.

Coolant Temperature Sensor: The coolant temperature sensor helps the ECM adjust fuel delivery based on engine temperature. A malfunctioning sensor can lead to improper fuel mixture.