I bought a 06 duramax and love it for towing my fifth wheel. Not sure about all the emmisions stuff and what years are affected. I bought 06 because I did not like the new body style coming out in 07. I get around 12mpg while towing my fifth wheel. Around 16 towing my boat and depending on how I drive 19-21 empty and that is not pussyfooting it. Just got back from the Twisp area and a combination of driving on dirt roads (scouting) and windy 35mph roads and the drive home over blewett pass getting stuck behind traffic (speed up slow down) passing when you can by flooring it to get around the motor homes etc I averaged 19.1mpg. My old chevy 3/4 ton 6.0L gas got around 15 empty and when pulling my fifth wheel got around 8. Steep passes you just accepted 40-45mph. With the diesel no problems maintaining the speed limit.
Bret