[slowmover]

The difficulty of predicting tow mileage is the shape of the load, not the weight so much.

This truck type is fairly immune to payloads around 1,000-lbs, but then one must account for the number of acceleration and deceleration events. Payload is around 2,000-lbs.

If one used a U-HAUL trailer as control (the 6 by 6 by 12 unit; tandem axle) and kept the gross combined weight to recommended spec 2k on truck including trailer tongue weight and 4k on trailer, for a combination gross of around 13k one would have a setup for comparison across the other factors which go into FE comparisons (truck spec, climate, and terrain).

It's not the absolute number, it's the percentage change from solo.

Probably easiest to chart a two- hundred mile highway loop where the vehicle is fueled after about 30-miles, the test loop is run, and then refuel. This is a loop short enough that one stop suffices.

The towing rule of thumb is to deduct 30-40% from solo mpg over the same course with a travel trailer. That is with any spec vehicle; 1965 or 2015 MY. And it works well enough for an enclosed cargo trailer.

With the above trailer and the load stated over a seven hundred mile round trip I saw a deduction of just under 30% in a truck similar to Daves along the Texas Gulf Coast (warm climate and flat terrain). Known limited stops, the use of cruise control and at 58-mph.

Dave would likely not use CC, is in a cooler climate with rolling terrain, and would probably start from a solo mpg of 32+. I'd imagine he could keep the towing deduct to nearer 25% for the given load and his more challenging conditions.