Well a couple of month's ago I kept track of 2 tank's of gas about a week apart and I had 16.1 and 16.3 MPG. Now this is highway/city/local combined [NO OFFROAD] and I drive with a heavy foot [ last ticket was 20 PLUS over the limit] I always considered them suggestion's anyway !! Since then I've added a Flowmaster 40 series but I didn't track MPG with that alone but then last week I decided to remove the drawer on top along with the wind deflector. When I kept track a few day's ago I averaged 19.02 MPG. I put stainless bolt's with blue threadlock back in the 4 holes across the roof . Then I applied 4/5 coats of rust-oleum primer/touchup 2n1 bright white. Look's good to me. Not sure what did the most help but I'm guessing the wind deflector.