Hope things go okay Brian Mc...I talked with the Ford folks to see what was safe with my 2009 F150 (3.73, 5.4L V8, Max Tow Package) and here's what they said...10,700 was my "max" at sea level. Running safe, 75% of max = 8025. Then they said you have to take 3-4% horsepower in the engine off for every 1,000' above sea level. I live at 6,000' so my "safe" weight is 7,500#. I'm sure they went conservative, but I figured using 7,500 lbs was about right. I've been towing my 8316SS up and down the mountains and so far it's been great. I hit a 8% incline yesterday at 45 mph, my tach was 3,500-4,000. I have taken it too far yet, but will in a few weeks. Good luck.
2009 Ford F150 Lariat
2010 Rockwood Signature Ultra Lite 8316SS
Momma, Two Boys, and Two Dogs