i would have the car put back on a lift and check that plug out its right above the o2 sensor on the driver side. i spent 3 months tryin to figure out what was wrong with the car after putting a new trans back in my car i replaced fuel filter, had the intake manifold off 3x, injectors were out and cleaned and still didnt fix it. i had it back on a lift and a buddy of my is a hummer specialist and i had him take a look at it on his lift and he saw the wire and pin was pulled out the plug harness we fixed the wire and it runs great to this day. that wire was for the speed sensor and it controled the fuel and what not at the motor. it would run great at low rpms soon as you stomp it it run like junk. another thing to try reach under the car and unplug the speed sensor and drive the car and if it runs perfect then that is your problem with that wire i drove my car with the sensor unplugged till i fixed it. i hope thats your prob man i spent 300 bucks on junk that i didnt need