Automatic Tranny Question

On a recent trip to the Rocky Mountains, I was driving some very steep, windy roads and 3rd gear in my '97 Jeep Cherokee was too high of a gear and eas casing me to use the brakes too much. When I would downshift to 1-2 to get second gear, the car would ignore my request for 2nd gear and give me first gear instead. Driving in low gear while maintaining the speed I wanted made it necessary to reve the engine around 3500 to 4000 rpm. The car has nearly 150,000 miles but the transmission has never given me any problems. Might this be typical for this transmission, is it an early warning sign or might there be an adjustment that could change it’s shifting behavior? I am trying to decide which car should be used for “Cash for Clunkers” rebate program and have either the '97 Cherokee w/ 150,000 mi or a Jeep Wrangler with about 110,000 miles. The remaining vehicle will become my trail machine but I don’t want to spend big bucks on a vehicle that will just shell out under a strain.

Thanks