Vibration on Initial Acceleration

Looking for a bit of guidance.

I recently replaced my transmission mount in an attempt to eliminate a mild vibration that I was experiencing (1) when the engine was cold, (2) was in reverse, (3) and on the break or coasting under idle power.

Good news - the new transmission mount seems to have solved that issue, however, it has uncovered a worse vibration...

The truck now vibrates under initial acceleration from a stop or very slow roll. No issues at normal road speeds (25/35), on the highway, or at a stop. When it occurs, the vibration seems to be at the same frequency as the engine RPM.

Notable/relevant vehicle details:

• 2000 XJ w/ 140k miles. AW-4 Automatic transmission.
• 2 or 2.5 inch lift
• transfer case drop
• (possibly) original motor mounts. They looked good about a year ago I had the motor out. They still look OK, but the bushings are at a bit of an angle because of the t-case drop
• new transmission mount
• u joints dont SEEM to have any movement in them
• exhaust hangers look good. I cannot detect a leak.
• vibration occurs in both 2HI and 4x4
• Cannot determine source of the vibration, but it feels like the front of the vehicle. I can feel it in the seat, petals, and steering wheel.

I plan to take a closer look at u-joints within the next week. Probably remove the front drive shaft then test drive. repeat for rear. But, I don't believe this is the issue.

Because this has only surfaced immediately after replacing the transmission mount, I feel that this is a big hint and can only leave a short list of things to check. What else do you think I should be checking?

Thank you for the help!

-same frequency as engine
-transfer case drop
-feels like front of vehicle

motor mounts would be my guess.

I had a similar problem that turned out to be a driveshaft u-joint on its way south. I can't explain why it would smooth out once things got moving, but that is how it behaved.

You have a transfer case drop but did you adjust the rear axle pinion angle?
In my experience, a 2" to 2-1/2" lift will require about 3/4" of transfer case drop and 2-4 degree shims, for the rear axle spring mounts, to get the u-joint angles right.