I would forget about the gas mileage and concentrate on the other parts of the equation that are more important to you. A Subaru wagon will pull a 3,000 lb. trailer and without the trailer it will get 30 MPG on the freeway.
The new 2014 Chevy 1/2 ton trucks are supposed to get the best highway mileage but personally I would always go with a Toyota truck given a choice as they are much more reliable over time. I have had many different trucks and 3 Toyota trucks with more than 400,000 miles on the Toyota's and over 180,000 miles on each and when I sold them they are all still working perfectly and that means everything in the truck and the transmissions were still smooth and no gear whine and tight steering.
I only had the scheduled maintenance done during all those miles with the Toyota trucks. I wish I could say the same about my Ford, Chevy, and Dodge trucks but they were not even close to the Toyota's in engineering, build quality, and reliability.