In 2 wheel no problem. When in 4 high going up small grade, hear popping sound, also in 4 lo. Chevy told me that this was normal and this is one of the characteristic of the Allison tranny. I have 226,000 miles on truck and didn't have problem until 176,000. Had differential and transfer case taken apart and they found nothing wrong. ANY suggestions?:eek:

never heard a popping sound but mine will whine sometimes, could it be a Ujoint???

Are you sure the front wheels are actually pulling? Front diff actuator could only be partially engaging or not at all. I would jack up all 4 tires and run the the truck in 4wd with light brake pressure and see what happens.

Checked the u-joints and they are fine. When going up small grade you hear a pop or a jerking action. Had the rear differential and transfer case looked at and all ok

Are you sure the front wheels are actually pulling? Front diff actuator could only be partially engaging or not at all. I would jack up all 4 tires and run the the truck in 4wd with light brake pressure and see what happens.
The front wheels are pulling, still don't kow what the problem is. Chevy said this is acceptable to this truck. A bunch of Horse ___.

Chevy said this is acceptable to this truck. A bunch of Horse ___.

no its not accepable, ive taken my truck in places you woulnt belive 4hi and 4lo geared down into 1st with D lockedout and never heared any popping but it has jerked a little bit in really slick mud on a really steep grade when i was riding the brakes but it wasnt bad.