Pretty basic just drop your drive shaft grab a hold of the dang thing an see if you can wiggle it side to side or up an down. Also you can drop your drive shaft, jack up your rearend, and put it on jack stands and have a friend spin the tires while your listening for grinding. Im going to guess most of your vibration problems are from not having a SYE an CV drive shaft. I had some pretty bad vibration as well with my lift and tires ( 4inch lift, on 32s ). Cant say for sure if my pinion bearing was part of that problem cause I serviced the entire rearend when I did mine. IF you do plan on installing your SYE yourself I can not stress enough how much a good QUALITY pair of snap ring pliers are important.