Recently installed new injectors and air bags at same time. Started to notice vibration during acceleration from rear of truck w/trailer right away. Thought air bags were causing vibration under acceleration, took them off and still have vibration. Symptoms seem as if tire may be out of balance but had all balanced and rotated. u-joints and carrier all seem good, tranny mount looks fine. I have had u-joints go bad before and this is a slower vibration. Only does this with trailer of 5k weight plus while accelerating. I am guessing its not trailer caused as 2 different trailers (both gooseneck) same symptoms.
Any ideas, heading out on vacation Friday and would like to get fixed before I leave.

 

is the truck sagging under the weight of the trailer? that will change the ujoint angles and may make vibes

 

One of my trailers will set down on the timbrens the other will not with about 1" gap between timbrens and plates.

 

Check your serpentine belt and tensioner

 

a bad steady bearing (where the 2 drv shafts join) will show up as a vibration when a heavy load is placed on it, ie quick acceleration or heavy cargo/trailer
also check u-joints with the rear-end in the air(jacked up) to eliminate any strain

 

after I lifted my truck I noticed the same symptoms. I believe my issue is the axle housing rotating under load (raising the pinion) causing a more dramatic U-joint angle.

 

Thanks for all of the replies, I have not changed the angle or lift of the truck -- still factory and not going to change. I think I will put in new u-joints and carrier tonite - still factory non greasable so prolly should change anyways.