It has had a 4" lift on it for a year now nothing but replaceing the transmission mount on skid plate has been touched and it helped alot but still have the vibration at 40 to 50 mph
Does this happen at low rpms? If so, It's probably drive-line related. actually, it's probably drive-line related anyway. If, it can happen at higher rpms also then it may be steering related but you'll have to provide a bit more info.
Rpms dont seem to affect it really just like i said at that speed its real rough after that it smooths out
Well the reason I ask is after I installed my 4" lift I got some pretty bad driveline vibes at a particular speed but the effect was worse at lower rpms. So, it could very well be your pinion angle. However, it is not uncommon to have loose steering components causing some noticeable vibration at particular speeds. Its really hard to tell unless your driving the vehicle but that may narrow it down some. By the way do you have an sye/transfer case drop installed? that would obviously eliminate the first option.
OK after carefully re-reading these posts, I'm about 90% sure its the pinion angle. I remember after reaching a certain speed I would "get out" of the vibration zone. Also you would feel the vibrations near the rear of the jeep. I only reserve the 10% bc it seems as though the vibrations just started although you've had a lifted suspension for over a year which seems strange. Vibrations and frictional wear are THE causes of mechanical failure so, the fact that your just experiencing vibrations means something is about to go. Whether it be a pinion seal or something catastrophically fails, your driveline components are most likely under too much stress. Next time you get a chance, see if your loosing any fluid at the t-case or pinion seal as that will probably be wearing out first. Next, I would correct it with a t-case drop (easy to home-make) or an SYE adapter kit.