You'll have to take the claims of towing like it's not back there with a grain of salt. My four Cummins Rams towing near or just over their tow ratings saw peak hp rpm on interstate grades and bogged to 58~mph with foot to floor. That was 2600rpm with the 12v and 2900rpm with the 24v Cummins. Here is an honest video of a 6.7L PSD towing a 13-14~k lb toy hauler in the mountains. Notice 3k rpm and 58mph up the grade. Won't hurt a thing. If it does or the truck runs hot, it's inadequate for the job. You'll also notice the Youtube vids that claim O/D and 65mph up the grades never show a trailer in the mirrors. That's because they aren't towing anything. Diesel tales are like fish tales. There's more BS than truth. Keep it within the manufacturer's ratings, let it run in it's normal operating rpm range and enjoy the ride.:C
http://www.youtube.com/watch?v=-_1ZefREs0Y
