That's interesting I wonder why 97 and newer would cause vibrations i know the bodies and all changed a bit but hmm.

 

98, have RE 3.5" SR lift (about 4.25" actual), NP231, AW4, 8.25 Rear

Had vibes initially, went away with a 1" tcase drop. Been meaning to get an SYE for 1.5 years ever since, but I'm like 15k miles on it and no issues I know of. I did just have to replace center yoke on the front DS, but it is also a 13 year old vehicle with 170k on it so who's to say that's age, lift or a combo.

 

01... 3" on 31s with no problems after almost 7 years

going to go 33s next, 2" coils w/ ACOS up front (3-3.5"), and 2.5 leafs w/ Iron Man Adj. Shackles in back (3.5-4"), and still going to see how that is before doing anything. a tcase drop is so cheap its hard to pass up even though you lose a little GC there...

 

CryCo changed the length of the output shaft on the back of the transfer case... made it longer, which effectively shortened the driveshaft, which, increased the angles. In addition to that, the longer output shaft became a more effictive lever, adding stress inside the case.
The vib's were more reconizable when these rigs were new and lifted, or low miles and lifted. My guess is that many folks with 3" lift in a post '97 rig actually do have vib's, but the higher milege of a 10-13 year old rig already has enough noises and harmonics at play that the vib's from the lift seem minimal, or are masked.
My .02

 

like mikexj1020 said. depends on tcase, rear axle and transmission. best combo (for less vibes) is manual tranny, 231 and dana 35. worst is aw4, 242 and chry 8.25. which is what my last two jeeps were. got vibes on both at 2". my buddy had a 95 with 3" lift and no vibes. but he had the ax15 manny, 231 and dana 35. had to shim the rear axle and drop the tcase a little and no problem now

 

FWIW, my 01 was lifted at 23K in 03

it has 86K on it now

still rides as smooth as stock

oh and its the AW4, 242, chry8.25 combo