drive train vibration

[Andre L.]

question for all wheel drive experts - i just picked up a 07 denali, its all wheel drive (all the time - can't shut it off), the vechicles drive train will slightly vibrate/shudder between 35 and 45 mph. The vibration feel like is comming from the rear of the vechicle, no sign of shake/vibration in the steering wheel feel while driving. It is mostly evident while driving straight under mild acceleration or climbing a small incline and it is the most intense at that speed, is it not felt below 35 and above 45. The vibration will show up as slight while under coast (decelerating) through this speed also. It will do it in more than 1 gear (havent kept it in the first 2 to try but definitly in 3 and up to od. Few posts on the net are pointing it to a u-joint, while some point to a vibration dampener (not sure if this truck even has one, more so mentioned on the 1500 pickups). Would like to know if anyone else experienced this type of problem and can shed some light on it. I read the post on the drive train shudder on a yukon xl but wasnt sure if it was an all wheel drive, and the post did not show a resolution. Thank you in advance for any advice on the matter.