Anyone with a cammed 5.3 run into this issue before? Had it happen on a Silverado back in the day and I don't remember how or if I fixed it. This is in an Avalanche. The truck has a small stage 1 btr cam I think. it chops decent for a while and than the timing drops about 5 degrees, the fuel trims change a bit and the chop goes away. The idle kind of just smooths out for a few moments and then starts to chop again. Anyone have something similar happen? Any ideas?