Bad Vibration

I have a 1998 jeep tj 4.0 5 speed it has 4" lift and a spacer with 35" tires it has a bad vibration in 2 nd and 3rd gear about 30 to 40 mph and if you let off the gas it will stop but soon as you give it gas it's right back i don't know what it is but it will shake the crap out of the dash I have replaced all u joints and rear drive shaft ltanking it was that and it is not any help I will try it out it is so bad you can't see any thing out of the rear view mirror thanks matt

Does transfer case have a Slip Yoke Eliminator installed?

id say you need a slipyoke eliminator based on the transfercase drop bracket that you have.

also could be pinion bearing or rear pinion angle.

Can you take some pics of the driveshaft and of the rear pinion angle?

What about the angle on the pitman arm? Did it start after you lifted it?

4 inches is usually the most you can go with the tcase drop so to have the 4 plus a spacer id say your rear dshaft isnt happy. Not bad joints...but bad angles. What kind of lower control arms do you have installed?

On re-install, did you clock the driveshaft properly?

We've installed countless 4" kits on TJ's. Your going to want an SYE kit, CV Drive shaft and a set of Upper Adjustable control arms so you can dial that pinion angle in where it needs to be on the rear.
Good Luck,
Bobby
CCOR