20 city/28 hwy is pretty good. Sounds to me like you're sorting it out pretty well - already above EPA for both figures. Send me a private message if you'd like to set up a day/time to go for a drive. I'd be interested in seeing how the cyl-deactivation works in your van.
I see you put "Kammback" on your list of potential mods. I bet you've noticed the rear of the latest version of the van has a short OEM aero spoiler... baby Kammback:
