On original subject; U-haul trailers/tow dollies have surge brakes, which allows anyone to hook up, not just those of us with brake controllers in our vehicles. At ~2,000 lbs, for trailer, U-haul won't rent you one to tow a Ranger with a Ranger, but tow dolly is only ~750lbs which they would allow with 4.0/auto.
Rusty, you appear to need someone in your corner.
Let's "do the math" as suggested:
Output of Harv's 4.0 is ~240 ft lbs.
Manual M5OD is ~3.3" center to center of gears, so about 1,750 lbs force at pitch circle diameter (assuming same size gears)
5R55E as tiny gears with ~1.1" center to center, which would be 5,250 lbs force at pitch circle diameter, but we have 3 planetary gears , so force per gear is 1/3 of that - 1,750 lbs... darn that's close to manual.
But wait, we didn't compare that the M5OD has only ~3/4" wide gears versus the ~1-1/2" wide gears of 5R55E; but the teeth of M5OD are ~1/4" deep while those of the 5R55E are 1/8"...darn 3/4 * 1/4 = 3/16 in^2; 3/2 * 1/8 = 3/16. Son of gun, same number!
So, M5OD is remarkably close in strength to the 5R55E - as though Ford's engineers were designing them for the same application; who knew?
A torque converter multiplies torque to transmission, by "slipping" at lower revs. But by time you are at peak torque, it is "stalled" and no longer providing any multiplication. And while it is slipping, it generates huge amounts of heat. But then slipping the clutch does the same. Again, you should only be slipping clutch to get load moving, thereafter, it should be locked up.
So, I be in Rusty's corner, backing him on the opinion that it is Ford's corporate bean counter, being concerned that the "average" driver can't operate a manual effectively and truck might be back for warranty repairs (clutch) and corporate lawyer, being concerned accidents from the same (consequences of missed shift) that results in lower towing limits for manual.
If it was strictly the strength of transmission, limits for 2.3/2.5 & 3.0 should be same with either transmission, with only lower ratings on the 4.0 - where the higher power of larger engine would actually be limiting factor.
Note: For both manual and automatic, majority of driving would be in 4th (not supposed to use OD when towing) which doesn't use any gears.
p.s. Rusty, if you need help with the nurses while your finishing with the waitresses, i'm there for you, too.
Edited to add the detail that I had indeed considered that the automatic's planetary indeed divided the power over the 3 planets.