Gaining mileage while towing is very hard. We did not design the tow tune for economy, but with the extra power it will make it easier to tow. If you can keep you foot out of it you may gain mileage.
I always recommend to start off with the SC (superchips) presets with the GM's.
Use the towing tune
SC for the shift points and firmness
Stock on the speed and rev limiter.
If the tires are not stock, measure them from the ground to the top of the tire within 1/4" increaments.
Where do you live? Hot climate? I would go with the SC setting for the fans.
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