I know it is best to pretty much forget about good
Mileage while towing but just curious what others are getting. My truck is 2015 3.5 eco xlt 302a 157" screw sport.
I towed my new (to me) camp trailer home about 50 miles from the coast the other day. Road was a little windy with a couple hills and I saw anywhere from 7-9 mpg on the screen. I know the computer isn't the most accurate but it seems to be around 18-20 with normal driving.
Trailer was at probably 3k lbs and I had no one in the truck. I just didn't think it would more than cut it in half!

 

What engine/gears/speed/terrain?

That sounds about right for my truck when towing heavy through the KY/TN mountains at 70-75mph. Sucks fuel for sure.

 

3.5 eco 3.55 gears.

 

Just got back from pulling my SxS on single axle 14 foot trailer. Probably no more than 3,000 pounds with all the gear I had. I got 8.5 MPG rolling 70-75 MPH for about 150 miles.
2.7 crew cab 4x4 3.55.

 

I just pulled my new travel trailer home yesterday. It was 133 miles pulling a 6800 lbs trailer. My truck has the 3.5 EB with 3.31 rear end. I averaged 10 mpg. The truck also has about 13500 miles on it.

 

Besides the truck and trailer the terrain has a huge effect. Tfl truck did their 100 mile test that appears to be flat and I think they got like 9.6 or something like that with about 7000 lbs. behind it and I believe on the Ike Gauntlet they got like 3.6 going from 10,000 to 12,000' in elevation. I haven't towed my 6500 lb. travel trailer much with mine but with my '02 Silverado I got around 9mpg on the freeway, it'll be interesting to see what this new truck does.

 

My 213" NA, with 3.73's gets 24 mpg. Towing a 1800 lb boat it's down to 15-16 mpg.