I have a 01 gmc and am thinking about getting a new truck. What is this regen after reading it seems to drop milage. I like my milage i dont want a truck that will not get around 19 mpg.

if you plan on getting a brand new truck there is no way around it....unless you buy a left over classic.....orrrr you could cut out the dpf like some have...personally I like my 100k miles warranty just the way it is.....I am gettin close to 16mpg with about 6k miles on the truck...

I would personally wait for the 2008s to come out. Ford, Chevy and Dodge all have things to correct with this being the first year for emissions on a diesel. Its only another month or so. Still dont thing your are going to get as good mpg as you did with your old diese even with a 08 model. Its like putting a converter on a car, (10 fold) its way to restrictive to get very good mileage.

What is a dpf?

diesel particulate filter....check out this thread it explains regen....regen occurs in the dpf http://www.dieselplace.com/forum/showthread.php?t=158746