Have you checked the coolant temp sensor resistance when cold its the 2 wire one by the thermistat housing also check the intake air temp sensor its out by the MAF two wire unit also,if you have a scanner that reads real time data you could look at all the values and see what the computer is seeing

 

My 96 Chevy 1500 is showing po300 engine code need help

 

Thats a general misfire.

 

I've changed coolant temp sensor. Had a friend hook up to real time scanner and the computer found nothing wrong going to leave with him for a few days will let you all know ifi figure.out what is wrong.