Frog3151

im new to this page, i have a 2014 gmc sierra, reklez in pearland installed my 3/6 drop with mcgauhys everything. i have the slight vibration @ around 50 mph when excelerating hard. ive been reading about shimming the rear end or shortening the driveshaft about 1.5 inches. my question is, if i shim the rear diff where do i put the shims? can someone post a picture of two please. besides the vibration everything else is great. im also running 22" dub ballers with 284/45/22 with no rubbing in the front at all.