i have a 95 jimmy 4.3l automatic trans 4x4 when i start the truck cold it runs fine gets up to temperature then about 5-10 minutes later while driving it the rpm go up and down it starts to loose power backfires constantly and dies. if i let it sit for 30 minutes it will run fine again for the same period of time. i have put new o2 sensors in it, new plugs,wires,cap,rotor,icm,brain box. im getting frusterated maybe you can figure this out? any help would be awsome

 

Check engine light on??? Have you cleaned out the EGR Valve?? Is it an OBD2 engine or OBD 1? Look on the radiator reservoir on the passenger side is the ECM on top of it?? If so it is OBD2 if not OBD1.