I have a 2004 TJ, and i had the same problem. I took it to a buddy of mine and he did some looking around. Turns out it was both unions on my rear drive shaft. He replaced the both and it never felt and drove better. Also, to let you know what my jeep was driving like: when i would go into first, the stick shift and the jeep would shake...as if the clutch was bad or something...at least thats what thought. But turned out to be the unions on the rear drive shaft. For labor and parts it was about 60 bucks. Now if it's your front drive shaft unions, you better be ready to throw any where from 350 to 450 for repairs. You might as well buy a brand new front drive shaft instead of replacing the unions because the labor involved in replacing them will come out to be near that amount. Hope this info helps.