JMHO, but since you are on the highway towing 80% of the time, you might want to consider the M/S series tires over the AT's.
The width is a non issue when discussing these two sizes, but the added height will help you lower your RPM's a bit. Empty it will definitely help your mileage, and with 4. 10 I don't think it will matter even towing 11k.
You can't go wrong with the Michelins.
-Ryan