Towing up grades with "M" and 1 gears

Thanks Grit Dog for your post. I see this thread turning into my tow haul is better than yours kind of thing. I tow with a Tundra. I have over 50K miles on my current trailer that we have pulled over passes in Canada, Washington, Montana, Wyoming and other places not as dramatic. The first thing I do when pulling away from home is to shift into S5, which is the same as M5. This locks out the overdrive in my 6 speed tran. Engaging my tow haul basically changes the shift points. This helps when accelerating if you are in a hurry. It also uses more fuel so I usually don't engage this. On downhills, it holds the higher shift points which, I guess, helps in braking but only minimally for my observations. Going uphill I will often sift into S4 to keep rpms up. There have been some very long steep grades where I select a lower gear in order to keep my speed up. I can climb almost any grade at a min of 50mph. I find it even more important going down hills. I will anticipate the speed and downshift to increase engine braking. It works for me and my setup. I also prefer this method to waiting for the truck to roar as it shifts gears under load.