I picked up a misfire on my 2003 1500hd 6.0 when put under a light to moderate engine load mainly around 2500 rpm. Never got a engine code but with my live data scaner I was able to pick up #1 cylinder misfiring the most along with #5,#6, and #8 evey now and then. I took it to the gm dealer and they said that the crank sensor out of time with the cam sensor. The way I understand it all they did was reset the pcm. How does this happen? They could not give me a good answer. My friend has the same motor and year of truck and he has had the same issue. Sad part about it I change my spark plugs and wire again(only has 6000miles on them) and cost $150 and gm charged me $75 to reset the computer.