Trucks, guns, politics, HST vs Gear, orange vs green... some very interesting comments here.
I traded up to GMC 2500 to get better towing for my 7000 lb travel trailer. My old tow rig was 1500 class, had P metric tires, very nice ride, but was not as comfortable towing as we wanted. We had tried to do both daily driver for my wife and towing and it just didn't work as well as we had hoped. We have had the truck for almost 3 years now and I enjoy towing with it. We even take it on trips without the trailer, but we have a small SUV for daily driver around town..
I tell everyone I know that is truck shopping to get the highest number (lowest gearing) rear end you can. It ups you tow rating usually and will only help gas mileage. All the trucks you are looking at probably have at least 6 speed transmission. You have plenty of overdrive in transmission and by running the lower gears (wish I had gotten 4.10 instead of 3.73) you get more use out of the 6 speeds in the transmission.
I recommend 250/2500 series for your 8500 lb trailer, unless you are also commuting with it. If you commute daily with your truck and only tow a few times per year (and not in the mountains), then you might be happier with the 150/1500 series.