transmission shifting to early

I have a 92 cherokee with the 4.0 engine, aw4 transmission and NP231 transfer case. Last weekeing while coming down a steep grade on a trail near my house I shifted into 4lo and put the transmission in the 1-2 position hoping to use the gearing to slow my descent. Problem is once I started downhill after about 10 feet the trans shifted to 2nd gear and I had to ride the brakes down. This happened two more times and finally on a 4th hill the transmission stayed in first. Usually if you want to get the tranmission to shift to second gear you pretty much have to red line it, but this time it shifted into second gear at a low 1200 rpm just as I started to roll downhill. Any help would be appreciated

That's typical for the AW-4. There are a brazilian posts about rewiring the tranny to prevent that. Search "tiptronic" as one possibility.

Jim www.yuccaman.com