D20's don't last long when you are in low range...torque multiplication is a D20 eater.
Go with the Atlas if you need the lower gears otherwise to 205-which are almost bombproof and thousands of dollars less expensive.
I grenaded D20's like there was no tomorrow. I NEVER bounce or hop when wheeling, they just grenaded due to torque when climbing due to extreme traction and tire size.
The output shaft is extremely weak. The low range gear teeth are less than HALF the width of a NP205 gear teeth-I've got pics and the difference is impressive.
The cases are weak. IF you put a lot of stress on the case they will crack. I'm not talking dropping onto a rock and cracking it, I"m talking crawling up a waterfall and "CRACK"...it just let's go.
Go 205 or Atlas. I removed my Atlas and run a 205 behind my Klune 2.7:1 doubler now.
I use the throttle a lot on sand and snow but there's absolutely no comparison between torque load on sand compared to Moab slickrock.
Also, I ran a 21.5" long rear DS behind my ZF/203/D20 for 12 years with a full 14' vertical suspension travel and had 31deg on my CV...no issues. Run a GOOD antiwrap bar or 4 link it.
Good luck