That doesn't sound right. We go that way often. I don't have any magic I just let the motor and trans do the work. I'd rather be going a slower MPH but rpm's higher because I'm in a lower gear. Than a higher speed and rpm's lower. Higher rpm's equal more fluid (trans, coolant)circulating faster, and getting cooled more by what manufacture put in for cooling. Of course you don't wind it up the rpm's as far as you can. And those people that stop at the top by ski area and idle or shut down everything are doing exactly the opposite of what there rig was designed for IMO. Keep fluids flowing and air coming thru fins on coolers. You don't sound like the "be first one top of hill" type. Let the equipment do the work, that is what it is made for. And of course others on here say that fluid doesn't care what rpm your going and doesn't make a difference.
I leave my driveway in a 2003 with 13,380 pounds in a little 5.4 gasser with over 100,000 miles on it and have no problems. My poor little thing barley gets enough speed at end of on ramp sometimes. It is not a ball of fire by any means, but get the job done.
Many times (during our rainy season) we go over to Fish Lake or Leavenworth area just for the day or couple 3, to get some sun.
Yours equipment new and I've heard (but have not checked out) that many new rigs can run higher temps in trans due to fluid type. Maybe your temps are alright for newer fluids and everything is normal????
I'd do some research on what you describe because there are other places that make Stevens pass look like kiddy's play.
2003 Majestic 23P... Northwest travel machine
2013 Arctic Fox 25W... Wife "doll house" for longer snowbird trips
2001 "The Mighty Dodge"... tow vehicle for "doll house"