My Brothers car is still not running good.

[grandprixgtp_91]

Well my brothers 91 GTP is still getting really harsh fuel milage and is slow, it only has about 6,000 miles on the rebuilt motor ive put in newer injectors, replaced a few important sensors and he got a chip from Ben and it still does 0-60's in about 9.7 seconds, my grand am is faster than it. i dont know what to do, i just had it e tested and it passed with flying colours, and it has a high flow cat on it. optimax rebuilt this motor. i cant remeber who but someone here used to work for optimax, did they rebuild 3.4l dohc's with all the proper parts? i doubt that is the problem but im stumped i dont know what else to do, im thinking about changing the knock sensor but id like to scan it first. how hard is it to change a knock sensorin an auto without removing the engine??
thanks

Jake

[gpse3400]

Drop the rear of the subframe to gain access to the KS. As far as power, either your rings didn't seat ... timing wasn't set properly and if that were true the engine would be running rougher than normal....