It's my ring and pinion that went. 100% sure now. That left side climb isn't overly difficult, but there are some really big rocks and I'm not sure what I could have done differently.
I was slow climbing over the large boulders at the top, I *think* what I did was hang up the rear a little, and when I added power to climb, the right front went in the air, ATRAC searched for power at the same time as the right front tire hit the next big rock and grabbed. I thought I heard plastic rip or snap. That was the pinion gear spinning.... The 35's I have coupled with the lower psi and big lugs of mud tires were just a little too much. They grab a little too well and unfortunately, the weak link in the 100 is the ring and pinion.
Pretty easy to figure out now, I was frustrated yesterday and didn't take a minute to think about what I needed to do to figure it out. Isolate the problem first which is what I did by pulling the drive shaft, then the flanges. Then work down the list of possibilities.
When I grab the tail flange of the differential and spin it, every rotation has a bind that I can get through by turning a little harder (that would be the broken teeth on the pinion gear) and at 4.1 turns of the flange, it totally binds up. That would be the broken teeth on the ring gear meeting the broken teeth on the pinion gear. 4.10 gears. That's where my break happened. Or, another way to think of it would be $700 for every turn of the pinion gear (insert crying face)
I'm going to drain the fluid today and see what I find, but I know what it's going to be..... teeth. It's a really bad time for this to happen.