Yeah, it isn't hard to beat the EPA numbers at all. They test "highway" at something ridiculous like 50 or 55mph anyway with the windows up, a/c OFF, and cruise control on. Completely unrealistic. But it is also very well known that diesels take a lot longer to break in and having the mileage increase up to around 50k miles is not unheard of before it settles in. You also could have gotten a particularly healthy tank of diesel, there are definitely variations in quality and that directly affects the mileage.
Further: You have to be consistent in filling it up, you can NOT trust the auto-shut-off in the handle, that will allow massive differences tank-to-tank because of variations in foam affecting the handle. You need to fill it up until there is wet fuel sitting in the top of the filler, drive a bunch, then fill to the same point and calculate what you just put in. If you can't see wet fuel sitting there and not draining down... Then the numbers aren't accurate.
Diesel doesn't expand, so you can fill it all the way up (used to be called venting) and know that the tank is completely full.