7100 lb-rated new Silverado towing 4000 pounds

Thanks for all the well written answers. My searches of dealer inventory show V8 engines with any truck with towing. That would compel us to buy the V8.

I bought lightweight wheels for my Cobalt and achieve 36 mpg consistently in the summer. However, this vehicle will have a lot of vacation-duty as opposed to commuting, so our purchase could and should be steered toward towing. In that case the towing fuel economy is a "lower" priority than climbing ability.