2000 cavalier mid range stumble

[Ratman667]

I have a 2000 Chevy Cavalier 2.2 OHV 5-speed with 91k.

When I take off from a dead stop, the car pulls fine, stumbles, then pulls hard again. I don't have a tach, so I can't tell what RPMs this happens at. The stumble feels like the fuel is shut off or someone is holding the brake.

I accelerate with about 25% throttle.

Engine modifications are: HAI and a PCV catch can.

Plugs and wires are AC-Delco and have less than 8 thousand miles on them (gaped to 0.050). I replaces both O2 sensors at the same time. The air filter is a K&N that is serviced every oil change (5,000 miles).

I am removing the HAI and catch can, to see if it helps any.

So far, I have cleaned the air intake, performed an induction service and visually checked the plugs. The only other remedy I cant think of is sending the injectors out for cleaning.

Any ideas?

Oh, I forgot to add, my gas mileage has plummeted. From low to mid 30s to mid 20s...