For what its worth ......I was having a similar problem on rear drive shaft u-joints wearing out about once a year. I consulted someone who is a "wizard" of sorts on TJ' s and he recommended switching to a "high speed" grease. I started using Lucas 10301 in the green tube. Problem gone!
Interesting, may have to get some greasable u-joints and go that route. I’ve been using non-greasable Dana ones.