Hello. My Silverado has a 350 vortec engine. When at or near highway speed, it will start severely missing, bucking, and hiccupping, most of the time under load (up hills) and even on flat roads sometimes. This always happens in overdrive. If I accelerate to drop to a lower gear, the missing problem goes away until it goes back into overdrive. This condition has been happening for over a month, and getting worse by the day. The truck has a recent fuel pump, and (1) O2 sensor (suggested by an engine scan as not working properly, so it was replaced), and today I replaced the cap and rotor. I don't know what else to try. Please help!
Sunday, April 14th, 2013 AT 9:11 AM