LIDR, welcome to iRV2.
If you scroll down to the Workhorse or the Allison Transmission Forums and use the "Find" button (type in "transmission temperature" or "transmission warning" or something similar), you will see others have had the same problem.
The same thing happened to us last year crossing the Rockies. We were climbing a long grade in 1st gear. Our Allegro Bay is 37 ft. long, loaded for full-timing, and towing a Saturn Vue weighing about 4000lb. We have the 5-speed Allison. Fortunately, there was a rest stop within a quarter mile. I pulled in, and by the time we had watered the dog and went to the rest room ourselves, things had cooled down and we were on our way.
I now take it a little easier on the long grades. I try to keep the RPMs below 3800. We crossed the Bighorn Mts., the Absakora Mts., and the San Jauns this year with no overheating.
Check the color of the transmission fluid on the dipstick. Fluid that has been repeatedly overheated will start to deteriorate and turn brownish. Both TranSynd and Dexron fluids are supposed to be bright red. If your fluid is still bright red, I wouldn't worry about it.
2015 DRV Tradition 375KPS
2015 Chevy Duramax 3500HD LTZ Dually
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