Duramax mpg's

[Joe67]

Originally Posted by sleepertruck72

I am considering selling my 72 C20 because of the 10 mpg that I am getting for a 05 Duramax. The owner selling it claims to get 25+mpgs on the highway
That seems like smoke up my tailpipe. Is there any Duramax owners that get that much out of it. Someone else told me that the Bullydog chip can get 30 mpg on the highway. I love my old truck so I would rather keep it and find out the hard way about the mileage. Thanks for any input.

Tough to justify that these days with Diesel costing more than petrol, by the time you go through the expense of the truck and paying more for the diesel fuel, is there enough of a MPG gain to justify it?