Finally towed something with it.
Between everything I had in the truck, and the trailer she had about 6500lbs behind her.
Power was great. I towed from North of seattle to eastern oregon, about 300 miles. Over snoqualmie pass, umtananum and manashtash.
Snoqualmie goes from sea level to about 3000 feet, nothing major, just kind of fWONking long. The hill starts at mp 25 and the peak is mp 53.
Manastash climbs to 2700 ft with a 6% grade
Untanum gains 2500 feet at 5%
The truck never had an issue maintaining 70mph, it would often drop to 5th gear on the hills, and on 1 occasion it dropped to 4th. I ran premium as recommended.
Truck averaged 11.4 mpg with the load behind it, at 65-70 the whole trip(speed limit) With just the empty trailer on the return trip home I averaged 15.6mpg. The truck averages about 18.5 on this same trip unloaded. I was very happy with it. About 2 years ago I took my 6.4L powerstroke on this same drive towing about 7k lbs and the truck averaged 12.2 mpg. So, given the cost of diesel, i'll keep my little v6...
FWIW when I wasn't pulling the hills the truck was doing about 13mpg on flat ground...