My 35d seems to have "loosened up" around 4000 miles, getting 23+ MPG on the last two tanks while struggling to get more than 22 MPG on the first few tanks. The weather has been no warmer nor has my driving style or conditions changed, so it seems likely that the engine is getting broken-in. I've read that the diesels do even better in warmer weather, so I'll look for 24 to 25 MPG in the coming months. Not bad for a 2.5 ton vehicle.