The steepest I have ever pulled with the 07 is a 7% grade in West Virginia with my 46 Cadillac in tow. She never lost any speed on the pull. It was snowing and the Caddy was a block of ice to boot. Gotta love a Cummins engine!

 

26% going over the Sonora pass. Towing only about 8-9000 lbs and another 500 in the bed. No big deal except stopping.

Safety, trailer brakes, and not breaking anything are much more important than speed.

 

The steepest grade that I know for sure was 6%. Its not particularly steep,but its full of twists and turns for 7 miles. The max speed you can pull it at is about 35-40. The road conditions just won't allow any more.

Eastbound on Stevens Pass is pretty steep. I'd say at least 7%. The issue with Stevens is the hairpin turn at the bottom. You can hum along at 55-60 until you hit the final approach to the summit. Then you have to slow to about 25 and just can't get any run at the last few miles. If you really want to hammer on it,you could probably hit close to 55 at the top. I just hit 4th and cruise up at 45 or so.

I've pulled my 11k lb fifth wheel up both many times.

I've got gauges in my truck now,so next Spring I'm going to hammer a bit harder and see just how far I can push it before the EGTs get out of control.

I know I've pulled steeper grades,I just don't know for sure what the actual grade was.

 

Coming from Alaska back to the states I hit a 9% grade. Truck pulled fine, kept it down in the 40-45 MPH range to keep the EGTs in check. Smarty on Level 3 (old school, aka the Smokey), and a 10K lbs V nose trailer in tow. I was playing vehicle tag with a Toyota Tacoma pulling one of those 5x8 single axles U-hauls. I'd pass him going up the hills, he'd fly by me going down the hills.

 

15% for me, empty though. On hill in PA we take (that was calculated off of distance and rise) couldn't find a place that has the "actual" grade. it might even be a bit steeper than that. Truck did good in 3rd, any higher it lugged (auto)

 

I have pulled Sonora Pass as well with a 5th wheel!