I've now got 2500 miles on my 2009 35d and am getting 27.3 mpg. I've been trying to keep the speed under 2000rpm. That is about 65 miles per hour. When acccelerating from a stop, I've been taking it easy and keeping the shifts at about 2000 rpm max. I've been putting highway miles on it mostly.
I tried driving about 75 or 80 miles/hr and the mpg went down a little to between 26 and 27 mpg. I'm wondering when it gets to 5k miles if the engine will loosen up a little more and get better mpg. I'll keep you posted.