get a friend.
Have that friend drive (roll Jeep slowly using the engine actually) your vehicle forwards then backwards with wheels at full turn while you watch the joints and shafts/yokes.
there could be many reasons your wheel is jerky when straightening out, and you should be able to get a real good look while your friend moves it around.
they will need to turn the wheels all the way in both directions.
I drove almost a year including numerous wheeling trips before I found the hairline crack in a cap on one of my spicer 5-760x.
I personally have done more u-joints than I care to remember on Jeeps. I only buy spicers for my own Jeeps but have to re-re-do (not typo) one on the rear of my t-case this weekend..and I think the spicer box I had said china on it so I may look into a high quality AMERICAN MADE u-joint in the future.
04 TJ "U" package
06 XK Commaddy 4.7