7100 lb-rated new Silverado towing 4000 pounds

4% unloaded is likely to convert to no difference or poorer fuel economy when towing and more transmission shifting and hunting.

On a trip where you average 15 MPG and over a 1500 mile trip you spend $400 on gas, how does a 4% savings of $16 fit in the overall scheme of things?

I would worry more about passing performance on grades and being able to safely merge with traffic while towing the trailer than on saving $16 on a trip.