Ok...so I've read, and read, searched, and searched, and I'm still not clear on the topic fully. I know that all the late model GM SUV/trucks have a slip yoke on the front of the driveshaft, and over time/miles it gets to where it doesn't slip so well and results in a bit of a drive line clunk. I've dealt with something similar on my F250 that has a two-piece driveshaft with a slip joint in the middle. Ok, so... I've read that some of the solutions, fixes, etc are... A new nickel plated yoke. Read than even some of the newer models came with one from the factory. Read that this fixes the problem, but it will eventually return. Racket ball trick/hack. Putting part of a rubber racket ball down into the yoke, thus providing somewhat of an insulated "cushion" so that when the yoke slips, you don't get as pronounce of a "clunk" Pull the drive shaft and re-lube the yoke. Now, here's where I get a little confused. I've read that on the 2wd models, just pull it, throw your grease/lube of choice in there, slap it back in. However, I've read that on the 4wd/awd models, you shouldn't do this because you risk contaminating the transfer case with the grease. That you're supposed to basically use the same fluid/oil you'd put in the transfer case, the factory stuff being called Auto-Trak II (AC Delco brand). Just looking for a little insight, personal experience, and ideally someone that has addressed the issue on their 4wd/awd model. Thanks in advance!