I went on vacation this last week towing my wrangler on my car hauler also loaded with the kids 4 wheeler and camping gear.Well i know my load was not huge but it is what i bought the truck for. I had to pull through the central mountians of idaho , the temps were 95-100 deg. I was impressed to say the least, the truck had stock programming other than a speedo change. I did hit 220 deg from time to time and the fan was in and out but not on steady. I ran the cruise on 70 mph going up the steep grades and the power felt awesome, the grade breaking feature takes some getting used to. I still get nervous when the tach jumps up to the top end while grade breaking. I am very impressed with the truck , the only thing that i wish was better was the milage while towing, i averaged 12 mpg.

We towed all over Pennsylvania and Ohio for the last week. Hit some fairly high OATs, (90-95), couldn't believe it didn't get silly hot as it did several times last summer. Maybe the last trip to the dealer truly helped. I hope so. We'll get the camper out again in a few weeks. (35' travel trailer, dual slides, ~10,000 lbs. loaded). It would be nice to see the gauge not move again and only hear the fan here and there...

I ran the cruise on 70 mph going up the steep grades and the power felt awesome,

Is this ok to do?

We towed all over Pennsylvania and Ohio for the last week. Hit some fairly high OATs, (90-95), couldn't believe it didn't get silly hot as it did several times last summer. Maybe the last trip to the dealer truly helped. I hope so. We'll get the camper out again in a few weeks. (35' travel trailer, dual slides, ~10,000 lbs. loaded). It would be nice to see the gauge not move again and only hear the fan here and there...

What did the dealer do to your truck?

I just got my GMC 04 2500HD 6.6L, everything stock, and towed my boat to the beach and back. About a 200 mile round trip with OAT's at 95. Truck worked great. Didn't even know the boat was back there. It's a 21ft Center console. With full tank of gas the boat weighs about 3000lbs. I averaged 13 mpg while towing. My Suburban gasser would have averaged 8-9 mpg. I am very pleased so far.

Your milage doesn't sound to bad to me. I have a 24' toy hauler that's around 13000 loaded and I get 10 - 11mpg.