Poor power

95 monte carlo 3.4, drove fine parked it week later went to start end rolled over hard and backfired, would not start rolled over like out of timing, installed timing belt, started right up high idle, then lowered but had poor throttle response, double checked timing off one tooth, re-timed started idled high then low still acted like miss, timing is right on, changed plugs, tried to restart wires are on right, the only way it will start is wide open throttle let off it dies but sounds like its running on three cylinders, good fuel pressure.