bad vibration happening as of today

hey guys i am having a problem with my 97 xj, here are the specs. 97 5 speed with 120k. three inch lift, 31" tires, transfer case drop, 3:07 gearing. now i know my gearing is bad for it but i tow a car dolly around with it and its never given me a problem until know. i was going for a 120 mile drive to drop my dolly off at a friends house and in the last 10 miles i started to get this strange vibration.
my steering wheel doesnt shake but i can feel it in the clutch peddle and the shifter. when i go faster then 40 i can feel it shaking the whole car and can actually hear it too. i looked under the car and nothing was noticably wrong. i checked the driveshaft ujoints and they were fine. the front dshaft had a little wiggle room where it extends. is that normal?
now i am leaving for 3 weeks tomorrow (in a different car) so i cant work on it but i gotta figure it out soon so i can make the trip back without the dolly. also within the last year all the tie rods, ball joints and ujoints were replaced. i had an alignment done last month. the vibration starts at around 30 and is the most noticable when i stop acelerating. t happens when i am in gear or not, clutch in or clutch out.

I always take one end of the driveline off to check cause there can still be a bind in it on the rig. Plus it makes it easier to check up close without having to strain to twist it.

I have the same kind of issue. Vibes at acceleration and vibes when I let off, but more of a grinding/vibe combo. I know mines the drive line angle because it did it the second I drove it after I installed the lift.

yea im gonna have to do that. it just doesnt seem right though. because it wasnt having any problem and then all of a sudden it was a severe vibration.

Dont know why it started later, but its most likely because of the lift. All the research ive done, everyone says 30mph. I have the tcase drop too, and it still does it.

SYEs are the way to go. I have one but it hasnt been installed yet. Since your at 3 inches, you could shim your axle too.

For the trip though, Id do what the last guy was saying.

Maybe since it just started doing it something bad is going to happen. Lets hope not, but wouldnt rule it out.

Check the u joints in the rear drive line. Also make sure the slip yoke is in far enough. Usually with a 3" lift it will back out about 1/2" when at rest. Should have about 2/3 of it inside the seal. If not, it will vibrate and take out the seal.

You should not throw shims and tcase drops at a lift indiscriminately. Get an angle finder and check the tcase and pinion angle and then match them to within about 3° or less. It needs to look like this:

well i took off the front shaft just to make sure. problem is still there. is it possible to have a bearing going bad somewhere in the driveline? caused by the extra strain of a trailer? the u joints are fine. i have had the lift 2 years. had a little vibe when first installed, the t-case drop took care of that. havent had any vibrations since then. until now that is. i have no shims.

Lots of tongue weight on the trailer causing the back to go down?

I'll take a guess that you have a 8.25" axle?