I live at 5k feet. Highest I’ve had the truck is over the pass through Rocky Mountain national park. I spend a decent amount of time at 7-9k.
no camper the truck reads 14.5-16 avg mixed town and highway. Loaded up with camper you’ll drop 1.5-2.5mpg. Kinda depends on what you’re doing. If I’m up in Wyoming with a stiff wind that could drop to 9-10 but that’s a pretty serious wind.
When I have the camper on I pretty much always drop the gear selector into manual ans just use gears 1-5. That way I don’t bounce in and out of 6th.
I actually have a new Tundra as a rental this week. 2021 SR5 crew cab 4x4. That truck is getting 18.5mpg in Maryland. I actually don’t like the truck. A pillars are big blind spots and I don’t like the interior. It does have great power though.