I did a leveling kit on my '06 Silverado because I was tired of it pointing down in front. Now it sits level with ground. It wears 33" tires and IMO looks pretty good. I did have to adjust the headlights for towing as they were blinding people once some weight was put on the hitch. Gas mileage sucked while towing to begin with. It's around 12 mpg and didn't change much from leveling.
NoCAL