Multi cylinder misfire

When was the last time it was tuned up? Also, these engines, in my experience, are picky about the parts that you put in them. I suggest using only plain old AC Delco plugs and wires that GM says to use. No "upgrades" like split fires or anything like that. Also, what about the distributor cap and rotor?

If you have done all of those things already, then I will ask do you find yourself having to pump the gas while starting it? Because these trucks have issues with the injectors (aka "spiders") where they can cause a random miss and make it hard to start the engine.

Let us know and we will go from there.

A simple thing to do would be to take the distributor cap and rotor off and make sure it is completely dry in there. Then file off any white-ish looking corrosion from the rotor and contact points inside the distributor. The distributor cap and rotor on that vehicle do let some moisture in sometimes, causing misfires. You could also inspect the contacts between the cap and plug wires looking for either (1) corrosion or (2) signs that the wires are getting too hot like rubber melting to the cap.

If this helps, then you will probably want to go ahead and replace the cap and rotor.

Keep us posted.