[Chevy454]

We've had a couple 8.1L rigs and 3 generations of Duramax trucks, and here are the general numbers I use when people ask about cost differences...

I've driven the same route to/from work (55mph speed limit, open highway) for 3+ years now, with 3 different 4x4 trucks...and I've kept nearly every fuel receipt I've ever gotten in this time. The 8.1L was a ccsb, and generally got 11-12mpg as a daily driver, and would *occasionally* slip in a 13mpg if I ran over to West Plains (25 miles of 65mph 4-lane)...and this was with an ecm tuned for mileage (Wait4Me). My LB7 Duramax was a cc/drw, and it would see 16-18mpg, but was a chronic injector eater as are all LB7s (unfortunately). My current truck is an LLY ccsb, and sees 15-17mpg, but will slip in an 18mpg if I see the 4-lane...dad's '06 gets nearly identical to my truck. Having said that, here are some numbers I use when people ask about cost to drive...

8.1L = $3.25/gallon, 12mpg = 83.3 gallons per 1,000 miles = $270.72 (regular)
8.1L = $3.55/gallon, 12mpg = 83.3 gallons per 1,000 miles = $295.71 (premium)
LLY = $3.75/gallon, 17mpg = 58.8 gallons per 1,000 miles = $220.50

The higher the fuel prices are, the more savings you'll see from the Dmax...plus, you can easily add a tuner that will gain mileage/power at the push of a button on the Dmax, versus the gas truck which will only see marginal gains. But, aside from the higher initial buy in price (you can really tighten it up if you buy used), you have the additional cost of 2 more quarts of oil at service time plus the price of a fuel filter every 15k miles with the Dmax. I loved my 8.1L, but my Dmax just does pretty much everything better...