The 42RLE trans has a lot of slip programmed into it. Since Old Stage has quite a bit of high grade ups and downs with hairpin turns thrown in for good measure, your Jeep spends a lot of time shifting (and slipping). This causes the trans to heat up. By putting it into 4LO, you will naturally slow down, IIRC this also reschedules your shift points for the trans, and since you're now putting more torque to the ground, your trans doesn't have to work as hard. Why would a Datsun 210 have an easier time on this road? I don't know; maybe because it weighs 1/2 as much, better gearing, manual trans, any number of other factors, or just because DC programmed too much slippage into the 42RLE.
