I got SES light the other day and the code was p0300 so I looked it up all it said was random cylinder misfire. It runs like crap usally when cold and under 2K RPM has anyone else had this problem? Also I have new plugs they were just regular OEM type. but do have the 8.5 MSD wires got both less than 2 months ago. Also its a 5.3L

 

I would check the wire connections.MSD's don't lock on that good.

 

The 99 year model had a problem with the charcoal canister getting water in it and it would have slight to major misses when it would rain. Pull the main line of the canister, by the fuel tank, and if even a few drops comes out you will need the updated canister. The water gets in the fuel rail and your misses are on seven and eight. The water pools at the rear of the injector rail above these injectors. Give it a shot. Oh you will need the updated hose also they come in a kit from GM.