I do something a lot like BigBen's technique.
I downshift to a gear I like by pressing the brake pedal. (BTW in newer coaches, mine is a 2019, the trans operates almost the same in or out of tow/haul going down hill.)
It's difficult to get the right gear sometimes, but practice doing what BigBen says.
What I do is set a target speed and a max speed. When I reach the max speed, I very lightly press the brake with my big toe - pretending there's an egg between my toe and the brake pedal. Remarkably quickly, the speed will drop to my target range.
The trick I had to learn was to downshift BEFORE I really needed to.
I really disliked this feature at first. It's taken some considerable time to adjust my thinking.
At 4k rpm, our Honda CRV just purrs along. But 4k rpm with the V10.... well...You have to get used to the engine sounding like it's screaming bloody murder.