And automatics just pull so much nicer than manual trans ....
That depends. The new ones are pretty good, especially those with a "tow/haul" mode that actually has some smarts behind it. The old skool 4 speed automatics with simplistic control strategies were awful, and some of them would grenade overdrive, or overheat, if the driver didn't know what they were doing. My own tow vehicles were manual, until recently, because I could do a better job than the old-skool automatics could, and not blow something up.
I split a ride to Jennings with sircastic (RIP) years ago, in his Ford Expedition 5.4, 4 speed auto. It would not pull overdrive with the torque converter locked with the trailer in tow. But it wouldn't do the smart thing, which is to downshift to 3rd but keep the torque converter locked, unless YOU locked it out of overdrive manually. Whole trip there and back with overdrive locked out (i.e. in 3rd gear), 100 km/h ... I called it the 5.4 that sucked gas like a 7.4 but felt like a 2.4.
The other nuisance is the tendency when going up a somewhat-steep hill while towing is to bog down in 4th (or 3rd), then downshift and take off, overshoot the cruise control setting, upshift, lose speed and bog down, repeat again until you crest the hill ...
Same trip similar trailer in another friend's newer Ram truck, 5.7, 8 speed auto ... not an issue at all. It picked the right gear all the time. Much more pleasant to drive.
My van (which has a modern 6 speed auto with a tow/haul mode) keeps the torque converter locked in the higher gears as much as it can, even after a downshift up a hill ... no overheating, keeps fuel consumption decent. It figures out when you are climbing a hill and disallows an upshift to a gear that it knows it can't pull ... cuts down on gear hunting. Going down a hill, it remembers the speed you were going when your foot came completely off the accelerator (even if you are not on cruise control) and it automatically downshifts if it goes much beyond that speed, to save the brakes. Some of the old skool "tow/haul" modes (*cough* GM) locked out overdrive ... this one will give you overdrive, with the torque converter locked, when it sees that it can do it.
Modern automatic, not an issue ...