I recently had the bump/stop problem fixed on an '04 JGC 4.0/Selectrac I
bought used and so far so good. The TSB summary I saw on the KJ website
applies to V8 models and talks about replacing the driveshaft but it
also contains a Note that on 4.0's the splines should be greased. The
service writer I talked to said it was very common, doesn't hurt
anything, and might come back eventually. They pulled the driveshaft and
greased it in about half an hour. Mine is still under the 3/36 warranty
so I don't know if the powertrain warranty covers it.

Mine would only do it after a delay or on acceleration after very gentle
stops, most of the time it happened as the rear end settled right at the
end of a stop. One way to confirm it's the driveshaft is put it in
neutral before you stop and see if it goes away. The service writer told
me a similar problem is sometimes caused by a bad ball joint between the
upper control arm and the top of the differential.

Also FWIW, there's a TSB on the '05 model that too much grease can
accumulate in the boot and cause a driveshaft imbalance condition,
something to remember if you ever fix it yourself.