Rear differential need rebuilt?
 

I have already changed the fluid and added friction modifier for the factory LSD and i think at 186k miles the rear end is just worn out. After a highway trip (40-50 miles at 70-75mph) the rear end chatters around low speed corners again (as if there wasn't friction modifier in there or something) but after it sits for a day that issue goes away. Now when going around corners or "sliding" corners in snow I am hearding a clunking noise that sounds like something is rolling around in the box (but there is nothing back there). Anything else I can do to correct this issue? Or is it just time to have it rebuilt? I am not even sure where to go for a rebuild as I usually don't trust shops to work on my vehicles (I do all work myself, with the exception of differentials and transmissions).

Your clutches might be going bad.

It is not that hard of a job to change the differential. You just jack up the truck, pull both axles, and take out the bolts holding the differential and remove. There is most likely a youtube vidio out there that you can watch to see exactly how to do it. Since you have an older truck, I would go and get a used differential from a salvage yard. These usually don't go bad unless they have a lot of abuse, they get water in them, or somebody changes the oil run them for an extended period of time without friction modifier.

I plan to keep this truck for a very long time, so if i go through the hassle I want a completely rebuilt rear end not a junk yard unit to get me by. I found a local place who I have heard great reviews about (I knew about them, but had forgotten because I always work on things myself) and they take pride in their work. $600 for clutch pack replacement, $1500 for complete rebuild (bearings, ring/pinion, clutch packs, everything) or $1800 for complete rebuild using detroit locker.

thats the attitude to have, I'm slowly beefing mine up with time. People here will obviously tell you to do it yourself but if you have never done a rear end rebuild you cant go wrong with having a reputable shop who knows what they're looking at do the rebuild. Piece of mind knowing it was done correctly and professionally.

replacing diff not rocket science but still not that easy, it a precision thing. Backlash and throwout must be dam near perfect.