So I had my first tow (not counting a small bass boat I towed a month back) this past weekend with my '08 F250. One word: WOW!
This thing is a towing machine! We just bought a new fiver (dry weight: right at 8k lbs) this past weekend, and we towed it about 120 miles home. This truck pulls like there is no tomorrow. It was mostly flat with some medium-sized hills (Lebanon, MO to central MO). I set the cruise at 68 and just let it go. It would downshift once on the larger hills and that's it. So much more relaxed towing than my '05 F150 5.4 and the 4500 lb empty travel trailer I towed with it. I am just simply amazed, and am SOOOO glad I went with the diesel. I am also impressed with how much more stable a fiver tows over a pull-behind. A world of difference, and a much better ride all around.
One odd thing I noticed, when in regen, when it would downshift going up a hill and hit ~2500 RPM, it sounded like the right-rear window was down. Very odd, but it only did it while in regen, and when the regen was finished, the sound went back to normal. That was the only way I knew it was in regen since I missed the popup message.
Fuel economy was just a tad better than my F150 towing the smaller trailer...right around 10.5 +/-. My parents were with us, and they were towing a similar in size/length/weight fiver with his new '11 F250 6.7L (600 miles on the ODO), and he averaged 2 MPG better than me (12.5 +/-). I guess the 20% claim is legit! Of course, they were behind us, so maybe he was drafting!
Overall, I am very impressed with this truck, and I can't wait to hook to the fiver again and take it on another trip!