UPDATE: I beat my own record:
This dispite the fact that it still hasn't fully warmed up yet this year. I even had a couple days driving through snow on this tank.
Here are the stats:
Start date: March 20, 2013
End date: May 3, 2013
Distance: 1,693.4 miles
Fuel used: 35.000 gallons
Total time (key-on): 64 hours, 46 minutes
Average ambient temperature: 49.0 deg F
Average in-cab mileage display: 50.92 mpg
Actual measured mileage: 48.38 mpg
Calculated average speed (from key on time): 26.2 mph
For this next tank, I want to break 50 mpg.