They are only worried about you wiping the clutch out during the warranty period. There is nothing else to it.
Tow whatever weight you want. Just make sure you get the clutch fully up before you start feeding it power. Get it moving, but don't try to accelerate until the pedal is up. And...not every modern transmission has a straight-through gear. Which means, I think, that the counter shaft, weakened by the gears between it and the mainshaft, isn't under a load in 1:1, or 4th gear. I think this is the case with the M50DR1.
My trailer is 2,000# empty (Load Trail equipment trailer with a single 7,000# axle) and I towed it with 240 sandbags full of mud during a flood clean-up with my '95 Ranger 4.0 5-speed. I work out with 50# dumbells doing arm curls, and these sandbags were way heavier than I could curl. I can do 60s a few times. These were more than that. This trailer was 18,000 maybe. I kept it below 45mph and in 4th gear. The trailer brakes are good. The little Load Range H 8-14.5 tires were sagging hard. The truck wasn't outside of its ability at that speed. It's not a little cantaloupe-sized Honda Civic transmission. It can do some work.