You may also want to find out how much ethanol is in the gas before you pump. Thanks to the fine folks at CleanMPG for making me more aware of it -- I had to ask the clerk how much ethanol was in my gas and it was 5.79%. But I like this station (fair prices, good service, close to home/on way to work) so I'll stick with it. Could be worse... could be 10% ethanol!!!
This could also be why you seem to be getting better results at one station over another... just something to keep in mind.
As for improvements, I recommend scangauge then belly pan. With the SG, you can actually improve your FE while driving or mods at that moment instead of waiting for a tank reload. Rear wheel skirts could also be on your shopping list of things to do in the future as well.
55mph may be fine for ROFLBOX -- he did say he was in BFE Iowa... which sounds like less traffic than what you may encounter. I can go 55mph on the highway around here as well but I have to be very strategic about it. That's why I prefer the intrastate side roads to get to work. There I can hover around 45mph and maximize those miles before I take the FE hits once I enter the city and all those red lights.
