Over the years I have played with the clearance over the cab. I have gone from 2 inches to 8 inches, with the same truck and TC. I know in theory it makes a difference in drag, MPG, and so on. But my real life experience suggest it made so little difference I could not tell by seat of the pants driving. I think I did get a few more bugs, but with 6+ inches of clearance they were much easier to wash off from the TC wall. It was also much easier to wash the roof of my truck and use the storage area in the bed of the truck.
