u-joint

I had a friend check out the humming/groaining noise from my front left wheel and he had said it was my u joint. it has an 1/8 inch give when you twist with your hand.
I'm not sure if he is correct but it does sound plausible. if so, is that something i should fixed right away or is it even the problem.
Since it is directly effecting the geartrain, would that be the reason for my auto trans to jerk a little bit when i put into drive?
Suggestions greatly appreciated

Groaning noise from the front could be a bad U-joint, this can be checked by raising the vehicle and with your fingers, move the joint up and down, side to side, if there is any play you will se it. However it sounds more like maybe a hub bearing gone bad. If the noise is at slow speeds and is constant while driving, I would say the hub bearing. It is something you can do at home, you will need access to an impact gun and a 36mm socket though.
Your tranny jerking, could be from the u-joints in the driveshaft to the rear axle. check these by having your jeep in nuetral, E-brake set, crawl underneath and move the jionts up and down, side to side, watching for play in the JOINT, not the whole driveline.

Huumm...
Fix the groan first...if you can get a lift, get it up and run it in 4wd.
Use a stethscope to check the wheel bearing and hub area. Then observe the action on the U-joint in that side of the shaft.
If you are sure it is not a tire something, start by taking apart the hub.