Originally Posted by Conanski

Check your ignition timing, factory spec is 10deg before TDC with the spout jumper plug pulled to disable computer advance, you want to verify the base setting but also that it advances some when the spout is plugged back in. It's also a common tweak to throw 2-4 degrees more advance in but be aware this puts the motor closer to detonation so you have to experiment a little to find a good setting, the way the truck is used and the engines condition all affect how much advance it will tolerate before detonation(pinging) because audible. More ignition advance produces more torque and horsepower, the difference in engine performance between 0 advance and 10-12deg is anemic to pretty peppy.