Just noticed ther other day on dry pavement that auto 4wd was on and in any gear at 4000+ RPM there was a surge release surge release type deal going on. almost like a A/C compressor cycling if that makes sense. The truck has probably seen 4000+ RPM in the last 20K miles maybe 4 times. Truck is a 2006 Silverado 5.3 4L60E 3.42 gears w/ 45K miles. Anyone ever notice this? Stock truck running a tune and 33x11.5x17 tires. Could this be a front u joint going out?

 

It would be a good idea to check both front and back,just to make sure.But yes,I seen some front ones cause that problem before.

 

Could be a dent in your drive shaft, u-joints, may have thrown a weight off of you drive shaft. Dont know much about the autotrack but that is what I have seen with other AWD setups.

 

I'll have to check it out, the truck does see a lot of jobsite driving so it's possible there is a chunk of mud on the shaft or I could have had it spinning in mud and slung the weight off as well. I'll check it out when I change the oil again. There is NO vibration in 2wd reguardless of RPM/Speed.