My father has a 2006 GMC Duramax and he said that he took it to the dealer under warranty and they changed a computer code or updated a program(whatever they do) and now he is getting reduced fuel mileage.

Just wondering if anyone else has had this problem?

Is there any way to get the previous program(code) back?

If not, what are the best programmers to increase fuel mileage?

elaborate on reduced....

never had this problem or even heard of it...but there are many tunes from hypertech and edge that will boost your mileage....i would also go back to the dealer and have them take a look at it and see what they can do

hope this helps