I'm having trouble diagnosing an issue with my 2000 XJ w/ AW4 and NP242. Anytime I drive with the gear selector in 3, which I sometimes do while driving below 50-60mph because I have 3.55 gears and 32" tires, I will hear/feel a single clunk or thud when slowing to a stop. The thump seems to coincide with the transmission downshifting into first gear.

I have an IRO hack n tap SYE installed, so greasing the slip yoke is ruled out. I have a brand new rear driveshaft with new u-joints, and a new Anchor trans mount. I've heard that the Anchor mount is junk, so I have a beefy trans mount on the way from user XJWonders. I also removed the front drive shaft last night, since those u-joints are worn. Clunk still persists.

I'm taking a fairly long trip to go wheeling in 2 weeks, and I'm trying to fix this before the trip. So far, though, I'm stumped. Any thoughts?

Try adjusting detent cable yet ?

Yup. I've adjust the TV cable a couple times.

Looks like the culprit was the slip joint on the new rear drive shaft needing grease.