I'm having the infamous grinding/slight vibration when decelerating. My rear diff is in the shop because the play on the pinion flange had about 10 mm (no in and out play) but when they broke into it and measured the backlash, it was fine (.006). So now it's just sitting in the shop collecting dust because we don't know why it would still have that 10 mm of play.

However, just out of curiosity, I went out to the garage earlier this week and found that the front and rear u-joints were notchy and didn't move smooth at all. I'm guessing a lot of the vibration is coming from those being dry (OEM with no fittings so I can't grease) and having poly mounts. Should I just have them close up the diff and give it back to me and just replace the u-joints or should I have them replace the pinion bearings, crush sleeve and set the preload? I'm looking at about $140 to have them just close it up and hand it back vs. $300 for labor + parts to mess with the pinion.

Also, the car has an aftermarket clutch and what I think is an OEM flywheel and poly mounts being the only mods. I ran the car with the transfer case out (which moves smoothly with no play btw) on jack stands and didn't have the noise/vibration so I know its gotta be in the driveshaft or the diff.

Well got my diff back this morning and got everything put back in. So far so good. All I did was replace my front and rear u-joints. Thanks for all the help guys.

What help

Exactly.