I got just under 24mpg coming back home before traffic came to a standstill on I-45. Not sure if the Gurney flap is doing more harm than good. It might keep the rain from coming off the edge of the aero cap and not gitting me soaked when I tuck up under the back end. I'll keep it on fer my local runs and see if it makes a difference or not. If it doesn't, then I'll probably take it off and see what happens the next time I make more runs to College Station.
Looks like my combined mileage is just over 20mpg. Still not too bad. I might git a few more chances to pull another trailer or two up to College Station. I'll do more data collection at that time and what changes I make to my truck.
I know I don't have a baseline...but there wasn't a normal trip pattern to develop before these runs came up. I just have to work with what I have.