Front end vibes

I have a 91 4.0 with an RE 3.5 lift. Alittle while back and all of a sudden I started to get a small vibration coming from the front end. I was told it was probly a bad front shaft since I have a locker up front and it started suddenly and after having the locker in for awhile. So I pulled the shaft and have been driving it for some time (with no vibration) until I had the time and extra money for a shaft. Anyways I came across a lightly used shaft from which the PO said only had about 2k miles on it and installed it this weekend before my snow run. Well the vibration is still there. I starts at about 45 mph, gets really bad between 55-65, and seems to settle out some around 70 mph. I have checked and tightened everything I could transfer case UCA's, LCA's, track bar etc. but cannot locate source. Anyone have any other ideas. Im stuck and really dont want to take this to a shop to figure out. Thanx in advance.

check your alignment.

sounds like you have DW...

could be the shaft, take it off and drive again see if it gives you the vibes. if not, take the driveshaft to a shop and have it balanced. also check all your u-joints.

alignment, trackbar, ujoints are good. The vibes stop when the shaft is off. Its not DW at no point do I feel like I am going to lose control of the truck. its just a fast vibe. I suppose the newer shaft could be bad but before I installed it I checked it and it is new. I have only had one wheeling trip with the locker and the vibes started months after that trip.

the shaft is probably not balanced properly. are you geared deeper than stock? is your pinion angle off?

make sure your pinion angle is close and get the shaft balanced.