You can try turning the pintle tip of the ISC to different positions as the other poster suggested worked for him, but I haven't tried that and can't suggest a method that would work other than what he posted.

You might try disconnecting the MAF sensor (in the air filter can) and see if it makes any difference.

Your distributor is different from mine and I can't help you with yours - Conner is familiar with it and perhaps he'll chime in here - hope so as his diagnostic skills are excellent.

If you have spark, fuel and air enough to start it, it seems possible that an electrical component is breaking down as current begins to flow. If that is happening, it's gonna be tough to figure out.

I assume it continues to run for a few seconds after you release the ignition key? If it doesn't and quits as soon as you release to the "Run" position, the ignition switch might be faulty. Otherwise, I wouldn't condemn the switch. How about hooking up your voltmeter to the battery side of the coil and see if you have voltage as the engine dies?

The power transistor (black thing next to the coil) is what triggers the coil - if you want to check it, let me know.

One thing you need to check is fuel pressure, but without a gauge and fitting it's tough because there's no test port. If you have or can borrow a gauge, you'll need a tee fitting. You'll have to release the fuel pressure, remove the hose fitting at the fuel rail and insert the fitting for the gauge between the fuel supply hose and the rail - otherwise you'll have to cut the hose, use a barbed tee and repair afterward or replace the pressure hose.

I can't help wondering about the ECU. I have read that it's possible for the ISC to cause the ECU to blow and installation of another ECU without replacing the ISC promptly caused the next ECU to blow as well.

I'd be tempted to make friends with a junk yard owner and try to arrange some parts swaps unless someone else has an idea. If you can find a like truck and get the ECU, distributor, coil, ISC, TPS, MAF sensor to try - and pay for anything that works it might be a faster way to eliminate some suspects - particularly if they're breaking down with heat. I hate throwing parts at an engine, but if it can be done without spending a lot of money it might be worth trying.

Frank