What your experiencing is known as converter stall. It is NOT a failure of anything.
You just don't have enough power to get things moving under a heavy load condition.
All the cures are $$$. They are......
1. Bigger engine, reduces MPG
2. A high stall torque converter, reduces MPG
3. A higher rear axle ratio I.E. instead of your 4.1 install a 4.88, reduces MPG
4 Fix your driveway, same mpg
The first thing to due is a complete tuneup on your engine to make sure its giving you the most power it can. Increasing MPG
Your starting with 108 hp and loose 3% for every 1000ft of altitude density. In the summer in Denver at 90 degrees your down about 28% so your working with about 75hp.