We have an 04 Dully that we towed a 20K lb trailer for 240 K miles before we took it out of service for an in town truck..... Trailer was rated at 24K with (2) 12K axles... . It made a run from Spokane, Portland, Sacramento, Bakersfield, LA, San Diego, Phoenix, Las Vegas Billings, Spokane at least once a month... we never had problems with the truck. It was slow going up the grapevine... If on a 100* day climbing that hill, we'd get close to another truck... . under say 60 ft the truck would start to overheat from the lack of good air flow... as long as we were 75 ft from the truck in front we never overheated... .
The trailer had power disc brakes... so it stopped...
There were some real issues in UT, MT, ID, WA in winter, ice and snow would sometimes hold us up for a day... . I wouldn't let my guys travel with chains, so if the chain sign was out they laid over... .
We now have a larger truck doing this run... . but it worked... we never had a problem at the scale houses with the proper license...
The only upgrade this truck has is a HD clutch, 19. 5" wheels and tires, PacBrake exhaust brake & air bags, and 120 gal fuel tank in the bed... .
We did destroy one NV5600 250 miles from home. 2 or 3 sets of Ujoints, 1 lift pump under warranty and on the next one we installed the in tank conversion.
This truck had no problem holding the speed limit in the states it traveled in... but slow climbing hills... .
Hope this helps... .