I'd scan the O2 sensor. Fuel mileage like that is often a dying front O2. Also on the evap leak...with the mods you have, I'd want to see if that appears to be modded at all. If not.. check your gas cap, evap soleniod (for a vacuum line break) and the evap canister that is located behind your driverside rear tire.

Kinda funny, I looked the code up for another local guy last night.

Being local, if this stuff continues...maybe we should hang out and see about figuring these things out. On the Aeroforce, check the power and fuse going to it. (at fuse box is the most likely place for an issue)