Damn, sounds like your getting great milage from your V6. I typically get 220 miles on a tank with 31" Mt's. It's gotten a bit better with the top end rebuild but still far from 300!
One thing to check on that lean code is the accordian part of your intake. I had to replace mine after a small crack formed in one of the ribs. It would only open up under heavy acceleration, barely visable. Had to take the intake off and flex it to find the leak. Acura V6 intake tube fits BTW. Dealer wanted WAAAAY too much for a new one.