Hi, we have a 1999 S10 Blazer 4.3 L motor, 4 wheel drive, automatic transmission, 176,000 miles. It has begun to have acceleration problems. The truck starts fine, RPMs are good. You can push the gas pedal all the way and it seems to run OK unti 25 mph, after which it begins to miss and accelaration stops. The truck does not stall, but is very rough. We replaced the fuel filter, also used fuel injector cleaner. Replaced cap & rotor. Coil test was OK. No check engine light. Any ideas?? Thank you!