Here is my experience--- I have had a 2011 RAM 1500 4.7 for 6 years. My travel trailer is right at the listed towing limit for the truck. I bought it when my tow vehicles was an F250 Diesel) I added Air Lift 1000 air bags just for an extra measure. I compared the build sheet of my truck to a friend's year newer RAM 1500 5.7 Hemi. I compared radiator, brakes, axles springs, everything I could think of that might affect the tow rating. The only differences i saw were the engine and the transmission.
On my first trip towing the trailer, I hit some "hills" on the original part of US 15. East of Chambersburg, PA, US 15 is a modern road with grades close to interstate highway specs. On these grades, everything was fine. Once you pass Chambersburg, however, the road reverts to the original US highway design and the grades were steeper. One grade was too steep--and even slowing down, the temps continued to climb with the "OVERHEAT" lamp ( I forget the exact legend because i only saw it once) lighting up just as we crossed the summit. Temps dropped immediately on the downhill side. I experienced no engine damage, but re-routed my future trips to stay on the Interstates with their better grades.
This Spring, during a heat wave and not towing anything, I noticed the temps rising. (I have an Ultra Gauge reader which lets me monitor lots of the computer functions--I keep water temperature always on display)--with outside temps approaching 100, the engine temp rose to 212. The normal range is 192-196. It was then that I noticed that I NEVER have heard the fan roar. (I used to have a F250 diesel and when that fan clutch engaged you could really hear it.) I verified that the resistance to turning the fan ( engine OFF!) was the same whether the engine was stone cold or up to operating temp.
I replaced the fan clutch. It is a quick and easy job--under 40 minutes and would be quicker if i had to do it again.
I immediately noticed the fan clutch when it engaged--not loud enough to scare pedestrians on the sidewalk, but loud enough to hear if you are paying attention.
I also installed and auxiliary transmission cooler, but once i saw the size of the oem cooler, that was probably overkill.
I just got back from 500 miles of towing in northern PA with no overheating at all--top temperature i saw was 208, but generally in the range of 194 to 198. That 208 was near the crest after a long climb. It was reassuring to hear the roar from the radiator fan.
I am no longer worried about towing at the factory limit. I think the fan clutch was the real problem all along.
One more thing--I have a SuperChips tuner and I used the 91 TOW tune fore the trip. This requires 91 Octane, so I blend equal amount of 89 and 93 octane. I averaged about 12 mpg while towing and 17.8 mpg otherwise.