I hope you bought the right model. LS1 PCMs only put out 1 or 2 tach pulses per revolution. You may have to set it up as a four cylinder tach for it to work correctly. My 92 six cylinder tach expects 3 pulses per rev for the factory tach and it reads way low when hooked directly to the LS1 tach output signal. If you bought a conventional style tach you will be best off to try it set up as a four cylinder module unless it was specifically designed for the square wave tach signal of a late model GM V8. The wire it will hook to in the PCM should be pin 10 on the red connector, white wire for a 2001 harness. I am not 100% sure of the wiring configuration on the 2004 since I won't spend $100 on a manual for a vehicle I don't own.