Yeah a blast from the past! MPG gains were great for the short time I had the cap. I was able to squeak out close to 36 MPG highway cruising at 60. My average commute was around 32 MPG, 40 miles each way with about 70% highway miles. I've since given the truck to my nephew, and all he cares about is shredding tires. lol
I tapered the back of the cap just to extend the trailing edge without creating a hazard to people walking near it. It was just an extension though, it didn't curve downward or anything. Plus, I thought it looked better.