I got 21.75 on my commute to work two weeks ago. 62 miles round trip for 4 days. Rural roads with three small towns and a city of Hershey to drive through.
I've got an Injen intake, a custom catback dual exhaust with a Borla muffler, the URD lightweight crank pulley, and electric cooling fans. And of course the TRD S/C, 2.2 pulley, and URD 7th injector.
I picked up a little with the intake and exhaust but I think the electric fans made the biggest difference. Freed up a couple hp and gained another mpg or 2. I also have 4.10 gears. I noticed you have the 4.30s.