I just towed a 5X10 6ft. tall enclosed utility trailer with one harley to Sturgis, SD and back I ran mostly 70mph. and gas milage dropped to 11 -12 mpg. With no trailer 16 or 17 is common with this truck. Should this drop in MPG be expected. 3200 mi. round trip. from WV.

 

Yes, that drop is average.

 

You just added 3000 pounds and a lot of wind resistance so, those numbers seem reasonable to me. But, I only get 11-12mpg empty at 80mph, so I'd love to get that towing.

 

Yes you have to pay for speed and weight...Check your air pressure with the trailer on and the tires cold...You may need more when towing...

 

I average about 12 mpg towing a double watercraft trailer. Weight is about 2000# and a much smaller frontal area with less wind resistance. I cruise 65 to 70 mph with A/C on all the time.
Mine is 4.6L, auto, and 3.55L/S. My trips are about 500 mi. round trip with lots of hills.

 

my truck is retarded, i get 11 mpg city, 11 mpg highway, and 10-11 mpg towing my buddys race mustang to the track, it is always the same have never figured it out