Just got done towing 620 miles with my 32 ft travel trailer. 11'3" tall. 9100 lbs. GCWR was 15340 lbs, on truck stop scale, prior to throwing another 100lbs or so of stuff in the trailer before I left. About 1300 lbs of tongue weight with full propane bottles. 1000 lbs LD bars and sway control. Average 62-63 mph and got 9.2 mpg on the computer. I installed a roadmaster active suspension for this as I knew I was going to be going too heavy for the rating. Truck has on the door sticker 14700 GCWR on the door and factory reciever hitch is rated for 10,500 according to the tag on the reciever hitch.
Prior to the roadmaster my ground to rear fender lip was 43 1/4". Never hooked the trailer up without the Roadmaster installed so don't have factory stock measurements when hooked up.
Installed the roadmaster and ground to rear fender lip 44 1/2". Front fender lip to ground is 40 1/2".
No LD hitch, Roadmaster installed and trailer hooked up my both front and rear fender lip to ground is 41 1/4" So the back squats 3 1/4 inch and my front came up 3/4"
LD hitch set and hooked up, Roadmaster on, and trailer hooked up my Rear fender lip to ground was 42 1/4 and the front lip to ground was 40 3/4. So from box stock truck measurement it only sagged and inch full hooked up with LD hitch and Roadmaster. 43 1/4 to 42 1/4. And the front only came up 1/4 inch.
Pulled great over a couple rocky mountain passes where my elevation peaked at around 7k and 6% grades on freeways. Would pull the hills at 55-60 reving around 4000ish and tranny temps peaked a 210. Flats it would pull in 6th but any incline I would shift back to 4th or 5th. Preferred manual mode over tow/haul mode.
For my setup and wind resistance of a 11'3" tall 32ft long trailer I want a little more power (which means I want boost)...... Its just a want and not needed if pulling at 65-70mph as the truck is capable.