One thing to keep in mind is the huge changes in the LDT. Most have had some form of exhaust brake since around 2008, and have had the Tow/Haul function earlier. These are huge changes from earlier designs when it comes to hills and grades and stopping.
Last year I lost the trailer brakes in the northern Canadian Rockies on a long 6% downgrade. It is in tow/haul, apply brakes firmly and downshift to 2nd (P-N-1-2-D) and let the engine control the speed. Hauled it comfortably about 400 miles that way to Whitehorse to get it fixed. The truck was an '07 Cummins and the trailer a 10,000lb TT. The cause was the brake wires in the axle tube, where they abraded and went to ground. Brake wires are now outside the axle and protected from abrasion.
This year we have taken a 15,000lb 5th pulled by a '12 Cummins from NW WA to Indiana, back to Montana, up to Alaska and back. We are in Southern BC with about 10,500 miles towing since April. I did put electric over hydraulic disk brakes on it and am using the factory controller. Now I have to keep a slight pressure on the accelerator maintain a speed of 55 on the downgrades. There may have been a dozen times I applied the brakes on a downhill in the whole trip. This ain't you pappy's pickup.
Having said that there have been improvements, the bigger the truck the better. We got an FL50 to carry her car on the deck and tow a TT, and she much prefers the pick-up as it is easier to get in and out of, easier to put her 'stuff' in it, and more comfy even though the FL is air everything. I like the FL for better visibility and better brakes, but the '12 Cummins has more power and handles the hills better both up and down.
