After the 1st 500, I put about 1,000 lbs. of broken up concrete in the bed and left it there till just the other day(10,500miles) just filled up and hand calc. is 21.6 with the winter "brew". Like they said, be easy the 1st 500 then load'er down, and let'er rip!

 

I bought my 05 with 26000 miles and it never got broke in , the MPG was low 12 or 13 mpg, I started pulling a 5000 pound loaded trailer on long trips for workand with in days my MPG went up to 16.5 mpg pulling and20.4 by it's self, both of these are lieometer numbers.

It jumped to 21.7 after I advanced the injector timing changing to the Rokk crank sensor by 2 degrees.

But like they said even if you have to borrow a trailer, load it down and drive a long trip at least a few hours without stopping and you willbe a happy camper and so will your truck