I have a 96 Yukon, throttle body and distributor run.

Yesterday the truck started stuttering on the parkway, then check engine started flashing. Clearly a misfire. Pulled a code P0300, Random misfire from the ECM. Took it to my mechanic and ran the SnapOn scanner and determined that all 4 cylinders on the passenger side were misfiring. Pulled the plugs and all 4 were fouled with carbon.

Since this engine is a recent crate engine from GearHead with a warranty I need to determine if this is an internal issue. My mechanic could not find any vacuum leaks or intake leaks. All fuel injectors are firing. No exhaust leaks.

Anybody have any idea what would cause one side of the engine to misfire and foul plugs out?