Guys not all jeeps are the same, some will need a 6 degree shim and others 4 or 8 even 10 degrees. I am not sure what came on your lift kit but that doesn't mean that it is the right shim for your jeep. When I installed mine I went through several before I finally bought the 10.00 angle finder and listened to what was being said, slowed down took some measurements and got the right shims along with a SYE and CV/DS. No more vibes for me. Or if you can weld you can cut off your perch mounts and set your pinion angle then re-weld them back in the right position. This is by far the best fix.
If you did not have the vibes before the lift install and are on the same tires then I am sure it is not the tires (more than likely). Also do a search for removing trac bars / sway bars.. Take both of them off both ends and throw them in the trash can or use them for scrap metal. If your jeep is setup correctly you will not know the difference with them gone.. I know that this is a heated subject and may cause some controversial debate but I think 80 to 90 percent of people on this forum that have been jeepin for years will agree to get rid of them. My wife drives my jeep almost daily on interstate and highways everywhere and has no issues with them gone. Best mod I ever did to get my jeep to flex and perform like it is suppose to..
Good luck and get an angle finder!!