I live in the foothills of the Sierra Mountains around 2,000 feet in elevation. We travel to Pismo about every other month for a few days of camping and riding at the beach. All the way there, I drive in tow/haul mode and love it. There are a couple of passes that I go over but shifting remains normal or as I would expect.

On the way back, things seem to change. Obviously I am gaining elevation. About 20 miles into the trip, I cross a 1,600 foot pass which rises and falls very quickly. Once I am over the pass and on level ground shifting goes back to normal and at 55 mph my rpms are below 2,000. However about half way home the transmission will stay in a lower gear and keep my rpm's up to around 2,500 - 3,000. I can let off the gas and it will stay in that gear and rpm range. I can top a hill and start down the other side and it will stay in that gear and not shift up. If I accelerate up to about 65 mph and let off the gas, it will shift up and my rmps will go down to below 2,000 and stay there until the next hill. My transmission will tend to heat up to between 200 - 230. If I take it out of tow/haul mode, it will shifts more often and will keep my rmps below 2,000 at 55 mph. Is this normal?

The shift points in TH are raised but I think that it should have shifted to the high gear by 55 mph. Have you tried speeding up to 60 or higher to see if it shifts up?

On edit I see you did and it shifted so I think it is normal, I just can't remember when mine shifts but it would be in the area between 50 and 55.