Accelleration problems

The truck ran fine prior to the engine swap. The old motor had 150,000 miles and needed to go. It actually ran really well after the engine swap (a couple years ago).

The back fire is out the tail pipe and is usually just one small pop. The symptoms are mostly a very sluggish acceleration, with hesitation until I get up to speed. Once I get up to speed the truck acts normal. I had it on the freeway today at speeds over 65mph and it ran fine. But when I get off and get to a stop light, I try to go and it hesitates and runs poorly until I get up to 15 or 20 mph.

My mechanic seems reluctant to clean the injectors manually. I think he may not have the equipment. His only solution (so far) was to add the fuel additive and ask me to drive it until I emptied the two tanks. I'm through one tank and so far nothing has changed.

Talked to my mechanic about your response and he said they did check the timing. They checked the spark plug firing, fuel flow, fuel line system, computer, and a bunch of other things that could cause the truck to run rough.

They also sniffed the tailpipe today due to the fact that I need to get it smogged for registration (California). He said it was running clean and that I should pass easily.

It seems to be running much smoother now. Not as smooth as my 2003 Tahoe, but much better than it was.

Thanks very much for your input!