LMM Fuel Economy

[vsp114]

2008 2500 HD crew cab, long box bought in March, don't drive it much yet, but with about 5,000 miles, getting between 17.54 to 18.81 hand calculated. Mixed driving.

[mesam57]

Just took delivery. 1 tank so far. Dash shows 14 - 16 in city. Highway driving can be good or bad; Seems the truck likes to run about 68 - 70 mph and 1800 rpm's. Running here the dash shows 22.6 mpg. Push the speed above 70 and 2100 - 2200 rpms and the mpg drops to 17 - 18 mpg.

I read about the priogrammers and the results don't seem to justify the cost.

I here (rumor) that the 2008's have a tattle tale in the on board computer. Do theses things void the warranty?

[Ric]

Well I bought the 08 Crew Cab short bed 4x4 chivvy with Duramax

Riding home the DIC calculated 22mpg with 1hr of freeway only driving... round town averaging with that freeway run over the next couple of days, the DIC is calculating 14 to 15mpg... Dunno bout the accuracy til I do some hand calculating to check GPS speed to the truck speedo and then hand calculate MPG...

I need to study this site more to find out about all the programmers etc because I do intend to run 305 70-17's on this truck

By the way, what is with the cooler thingy for the fuel being down near the ground in front of the fuel tank with no protective skid plate?

[Sivrug2]

There is a tattle tail feature on the LMM's that keeps track of the programming/flashes. This was relayed to me by the shop foreman and friend at the local GMC dealer.
I recently did a turbo back exhaust and installed a "Spare" computer that was programmed mild upgrade/tow.
Hand calculated my mileage in town is up 1-2MPG on the highway 5-7 MPG increase.

[Ric]

There is a tattle tail feature on the LMM's that keeps track of the programming/flashes. This was relayed to me by the shop foreman and friend at the local GMC dealer.
I recently did a turbo back exhaust and installed a "Spare" computer that was programmed mild upgrade/tow.
Hand calculated my mileage in town is up 1-2MPG on the highway 5-7 MPG increase.

will the tattle tale feature void my warranty if I install one of these programmers ?

[SlimWallet]

New 2008 GMC 2500 DC Crew cab....Colorado

First tank....mt, mixed town and highway.....16.2 mpg

Second tank.....mt... up the mountains to go fishing...mostly highway and 70 mph.....17.4 mpg

Hand calc'd

Slim

[Duramaster]

The ECM is supposed to keep track of the last 10 program reflashes.