I can understand your concerns about tire stability and trans temperature. I towed well over 300,000 miles on 265's with my LBZ pulling the biggest of the toy haulers cross country up and down the Rockies and never had a trans temp issue but I always towed in 5th gear or lower with the turbo brake engaged in the mountains. My ideal tow speed was 62 mph, anything over that and you could watch the fuel economy go out the window. I actually felt that the truck was more stable on 265's due to the larger footprint which you learn to appreciate in wet weather and the additional load capacity. They were always inflated to 80psi when towing, 70psi running empty. Maintaining proper alignment and tire pressure is crucial to stability and tire life, I checked mine every morning when loaded and was able to get 94k on one set and 92k on another set of 265's. The average fuel economy difference was negligible between the 245 and 265. However, jumping to 285's, you will see a difference in all 3, fuel economy, stability and trans temp as well as coolant temp in some areas during the summer. Average tow mileage was 10-14mpg depending on what was being towed, never used a tuner when towing, only when running empty.As far as going back down to 245s, I kind of feel that all of the sidewall, and having them blown up on the factory 6.5” wide wheels, is working against me a bit and not helping my particular situation. Plus, I’ve noticed a sizable decrease in my MPG and even a touch more heat in my trans fluid, just from the tire change. I keep an eagle eye on a lot more things that most will though.
Deciding on which tire to run is a big decision especially with limited experience with this tire or that tire. Elkhart is one of the most competitive tire markets in the country, 80% of all RV's produced in the U.S. are made in the Elkhart area and they all have to be outfitted and delivered somewhere. Michelin had a monster warehouse right down the road from the Discount Tire that most of us used. There were more than 20 companies at the time I was doing this and our company alone had over 1,000 drivers. I can only tell you what I experienced from actually doing commercial towing. I'm sure tire salesmen have their opinions and can quote what customers claim. I know what actually worked for me and others that I ran with. There are other haulers on this site, perhaps someone else will chime in also.
Good luck with your decision.