There are several reasons to drop your speed, not the least of which is safety. I see truck campers towing trailers here in Idaho every day as I work for the state highway department mostly on I-15. I get to push campers off the road into a big pile with a Cat 950 loader while the owners watch. This is heartbreaking to say the least. Most of these folks have one thing in common -- SPEED! Many overestimate their ability to control the truck/camper/trailer combination when combined with wind or sudden traffic stops. Be careful you don't become a statistic.
My 2016 Wolf Creek 840 weighs in at about 3000+ lbs fully loaded and results in my 2006 F350 SRW diesel weighing around 11,200 lbs., just under the 11,500 limit. The truck empty is 7800. It has the camper package. I added upper and lower stableloads to handle the extra load and have no need for any other suspension mod. It handles wind well, but there are times when I have hit 40-50+ mph gusts traveling across the high desert when I was glad I had Torklift tie-downs. It rocks the rig and sometimes surprises me, but it is controlled better when I am towing my 5X8 cargo trailer with ATV inside. Something about the towing weight makes the whole rig ride more stable, don't know why. Even mellows the bumps and bouncing a lot. It also handles wind better when the tanks are full.
My mileage varies widely due to wind resistance and truck speed. Unloaded I can see 17-21 mpg. Fully loaded I can get 12-14 mpg at 65mph, if the wind is behind me I can get 14.5. Increase speed to 70 and I get 11. Keep in mind my 6.0 motor is very economical and is in top shape -- I don't run any tunes on it. I don't drive faster than 70, so call me grandpa! The truck pulls Galena Summit near Sun Valley at 50 mph with TC and trailer without breaking a sweat, and would do it at higher speed if I wanted to kill any chance at saving fuel. Galena is 8900 ft. and very steep. My temps stay around 220-225 on that hill but would be higher if I stomped on it of course.
I plan on keeping my rig many years. I have 160K on the truck and can't afford a new one, so I tend to have very conservative driving habits. If you want to drive 80 that is your right and I support it. Doesn't mean I would recommend it. Especially after seeing this past summer's accidents. Traffic just seems to be getting crazier every day.