Today while traveling with a pretty good load up a mountain my truck downshifted and my rpms went up to @ 4K rpm my check engine light came on and it started to shutter. As soon as i knocked my cruise off and my rpms came down the light came off. My truck runs fine if i keep it under 4k rpm. Actually it normally stays under 4k but it was 2 big mountains. I took it to advance to see if they could read stored codes since the light was off now, but they couldnt with the one in the store but one of the guys who works there had one that could in his truck, however no codes were stored in my truck. Any ideas?

thanks

 

Could be a dirty fuel filter or a failing pump, in either case there would be a reduction in fuel pressure/flow during a higher demand time.

 

found out it was misfiring so i started changing the plugs and coil and found one covered in soot. plug wont come out. ill probably have to limp it to a shop.