Shaking While Tires Spinning!!!!

Hello there folks... I am trying to do a little bit of trouble shooting and thought you guys could give me a little bit of an opinion.
I have a 1997 XJ 3.5" lift 31" tires.. HAve owned the jeep for about 8 months now.... Seems to be strong and reliable off road machine. But I am now haveing some issues with shaking. The shaking only occurs when I am spinning in the snow/sand. My jeep is a 5spd manuel tranny and while the shaking is occuring the shifter vibrates quite a bit to... I think it could be the transmission mount on the cross member, Ive never had it apart to do a good check. BUt the motor mounts are fine and the shakking occurs in RWD and 4WD when I break traction and begin to spin. It's quite a violent shake though..... I also need a new track bar, the tierod mounting to the frame is very loose..... I dunno if this could have something to do with it.
Any opinions would be greatly appreciated ..
HAve a great day!

Park tour jeep up against something that will not move-heavy curb or something,pop the hood,load it up in first-don't melt the clutch to the flywheel or anything- and have a buddy see if the motor is moving excessively from side to side-, You can also see if the rear leafs are flexing causing axle wrap., definately replace your trac bar.Try not to run over your buddy

Ya, I'll try that when someone is here to help me, however I just had the motor out and I know the engine mounts are fine... And I added 4 leafs to each side in the rear for hauling a travel trailor so I don't think the leafs are allowing for any axle warp...... the noise seems to be coming out of the passenger side in both front and rear when spinning... thanks

did you retighten your u-bolts after 100 miles when you added those leaves?

Try a prybar from the crossmember or body to the t/c see how much it moves around, it should have some give but shouldnt move around much