I don't know how the other transmissions are setup, but the automatic in my Dodge is very predictable -- even in hilly terrain and can pretty much tell it what gear to be in. It's a 5 speed (3 speed w/ 2 OD gears). I can force it into 1 or 2 -- so that has me covered for those gears. I can shut one or both of the OD gears off -- so I can stay in 3rd gear going up a hill on the highway (or of course I can manually downshift into 2 if needed).
I understand the reliability concerns and granted, maybe I don't know any better since I've never towed with a manual -- but it's pretty easy to get in the gear I want. And even if I hit a hill in the wrong gear, I can easily correct that.
IIRC, some of the newer Cummins come with a button on the shifter to manually shift up/down as needed.