sounds like you installer didn't do his job right,8 degress with a SYE is a little much

 

dont know if this helps but im stock and get a slight wobble from 50-55mph and its cause i got a bushing thats going out on my front sway bar or somethin like that......check all your bushings

 

Big +1

The installer screwed up. 8* is way too much. Should be 3-4*

 

For the record it used to be 10 degrees and they took it to 8 and it got better.

 

then there is your answer

 

for reference i am at 6" of lift and i have 3* shims in my rear pack and have no vibes with a t case drop and a stock d shaft........i agree with the few others that the rear may be angled up too much especially for an sye, also make sure the front pinion is properly angled......mine was about 2* off when i first did my control arms because it was late and i "eyeballed" it and that caused alot of vibrations.....hope it helps some.....dont wanna be lookin for some problem that isnt even there

 

x2. lose the shims

 

yes, seems like the shims is your problem.
but, what sye is it, i think RE only does H+T.
maybe it's possible the shop didn't drill the hole dead center, or straight?

 

check your headlight fluid

 

i have a 6" junkyard lift and a homebrew 1" t case drop with a stock driveshaft.... no vibes... your situation just doesnt sound right to me

 

Lifts are not my expertise but I hope it all works out. I saw you said you were deployed. Thank you for your service to our country.

 

yeah and if thats full it could be a muffler bearing

 

 

dont forget the blinker pressure!

 

I ran a 5.5" RE lift with 2" spacers and the hack and tap with a 3* wedge and no vibes. 8* sound way too much to me. Bet the u-joint is trashed at this point as well.