Need a little help please. Trade my 04.5 for an '08?

[SStrano]

I know this is the 6.7 section, and I know that everyone loves the 5.9. I've seen the reports of terrible mileage on the new engine, but also recall seeing the same with the 600's when they came out too. I had none of those issues with mine.

What it boils down to is: I don't want a diesel hog. I have a 600 w a NV5600 w/3.73's now (Quad, SB, 4WD). I love the engine, the transmission has been a pain in my *** since day 1, and never shifted well at all, plus the headlights and seats annoy me. Those are all I hate about my current truck.

I'm considering the "same" truck, Quad, SB, 4WD, but obviously a 6.7, and with the auto instead. I can't see how a truck that turns a full 500 less revs can get such horrible mileage. It can't be displacement alone, Duramax's get good mileage @ 6.6 liters. I am concerned about this mileage thing, but know from experience you tend to hear more complaints than anything since folks often like to complain.

Is there anyone out there that has changed from 600 (or "610") stick and 3.73's to a 6.7 auto w/3.73's? Can you compare and contrast the mileage for me? I only know one person that has gone from a 600 to a 6.7. He's ****** about his mileage... but he also went from a SB 2500 G56/3.73 to a DRW 3500, long bed G56 w/4.10's. When the "old" truck was new he got around 14 and that got up to about 19 with time. This one is getting 12.5 so far... I'd assume (and maybe I shouldn't) that some improvement would come with time since his other truck got a lot better. I would also expect some drop in mileage with more weight and deeper gearing. Am I complete out to lunch here?

Looking for some real-world help on this if possible. Thank everyone (if anyone answers) in advance for any help. I'm just really torn... hard to pass up a lower payment for a new truck with more features (interior).