My brother and I both drive Chevy S10 ZR2s, 2001 and 1998 respectively, and they both have the same problem(s). Initially, the first minute after starting, the trucks will backfire and hesitate, which is most apparent when traveling up hill because if the engine hesitates when traveling up hill, we don’t go anywhere. However, after this initial minute, the truck perform just fine, mostly. The only time that they will not perform well after this initial minute is if we go to pass someone on the highway and need to accelerate harder to do so. If we do this, the same symptoms described earlier return, but they will not go away unless the trucks are shut off and allowed to “rest” for a few minutes. A similar problem was described in last week’s show, but that was for a carbureted S10 and I’m pretty sure that ours are EFI. Any ideas?
I would probably replace the fuel filters first as it sounds like it’s lean from your description. Engine size, mileage and maintenance that’s been performed would more than likely help.