99 express 1500 4.3L. Stopped running one day, found the computer to be a giant block of corrosion. Got a new one, had it flashed and ran for a few months. After it stopped running we replaced maf, fuel pump, several sensors hasn't run since.
got a 2002 same stats, gorgeous shape. Stopped running, new computer, ran great. Wouldn't start for one instance, after a few cranks it started. Drove home, shut it off, never started again. New computer, ran great for a few months, stopped running. Have replaced/checked every sensor. Crank sensor, distributor cap, and a bunch of sensors I can't think of. On last test, noticed, I don't think spark is getting to plugs, but getting to distributor. Could it be yet another distributor cap?

 

Welcome from Florida. I have had problems with off brand distributor caps and rotors. Some are very cheaply made that they don't last very long. Only buy good main brand ones like AC Delco.

 

You need to be aware of cheap poor quality imported parts. The boxes appear the same , but what is inside is cheap junk, a lot of it is defective right out of the box.
Best to stick wit OEM, AC Delco as stated earlier.

 

96-02 put the computer on the left fenderwell, which is a terrible place. Then they put it in an aluminum case. My 3500 when I got it ran fine until it rained, then because a hole was corroded into the case it filled with water and did all kinds of crazy things.

But the diagnose is the same as anything else when it quits. Start at the plug looking for spark and work back. Check for the fuel pump running and then check the pressure. Get a reader on there and check the live data for issues. Something as dumb as a bad coolant temp sensor can make it not run. A failed fuel pressure regulator can also do it.

If you have access to spares, even a you pull yard, get some parts there to use to diagnose before spending money on new.