I had an S10 Blazer come through my shop once that was behaving similarly. There were no codes, shook in gear but took off alright. It held it's gears though, which I felt was weird.
Problem was a failed MAF sensor. It was reading, but not the correct volume. Cleaning didn't help, but a new sensor had the truck behaving just like brand new again. I changed all the plugs, wires, coil pack, cap & rotor anyways though, they were factory originals with quite a few more miles than they should have gone
Mine's not showing any codes either... check engine light is off, and it passed emissions a few weeks ago with flying colors. What's the procedure for testing the MAF?
