Gasoline Mileage improvement after break in.

TomG2 wrote:
This is the first vehicle that I have ever owned, and I have owned many, that actually improved its fuel mileage a lot after the first 5,000 miles. It is a Silverado 2500HD with the 6.0 gasoline engine and the mpg has gone up from an average of about 14 to 16 mpg. I realize that diesels keep getting better and better, the more times this question is asked, but this is my first gasser to do this. Dealers used to promise this kind of result, but I was beginning to think that they might be misleading me.