I found a 15,000 lbs 4.86/6.61 diff on ebay in 2015 and installed it. Highest gear I could find. Runs fine but it dropped my GVW 5,000.
That's been tested a few times.
Honestly I just realized I don't know how to prove which GVW it is or isn't, I guess it cold be the full 20,000
J13 : 15000-LB. 2 SPEED AXLE 4.86/6.61 RATIO
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