I have a 94 gt, under acceleration it boggs then will run fine when the rpms come up, it will also backfire through the throttle body sometimes i have replaced the whole ignition system. i have cleaned the intake and throttle body. i have a few mods , cold air, headers, off road h pipe, flows, under drive pulleys, 3.55 gears. i have played with the timing and the backfire goes away but the car is very slow. any help would be greatly appreciated