First off i searched this forum for question or problems with Gm's active fuel management system to no discovery.

I 've owned my lmm for about 6 months now and have always ran about 80mph on the highway at 1800-1900 rpm's and getting about16mpg. This is of course empty with no towing.

Just yesturday I travelled from Baton Rouge and was running 80m.p.h. at 1200rpm's and improving to 17.5-18mpg under same load. I didn't notice any different dic indication or lights on dash to tell me I was running on 4 cylinders or not. How is this? Did I accidently hit a button and find another highway gear? I read the manual when i got home to find out my truck has a auto fuel management system. How is this triggered? What do you all know about this? I really got good fuel econmy on the way home. More than I ever got since i owned this truck. How is this?

UH....

Did I miss somthing? When the hell did the LMM get increased milage mode like the gassers? lol

To my knowledge there is no active fuel management on diesels; only the 5.3l . You may have it confused with active regeneration of the DPF

ok i know it sounds wierd, but I know for a fact that it felt like I was in a gear that I never knew I had. Like 6th gear for the first time.

I have a aftermarket turboback exhaust and quadzilla performance tuner set on number 4. Also a cold air intake, but all of this was done months ago. Is it possible then that my allison tranny is staying in 5th gear on the highway? Noone has expierienced this?

First off i searched this forum for question or problems with Gm's active fuel management system to no discovery.

I 've owned my lmm for about 6 months now and have always ran about 80mph on the highway at 1800-1900 rpm's and getting about16mpg. This is of course empty with no towing.

Just yesturday I travelled from Baton Rouge and was running 80m.p.h. at 1200rpm's and improving to 17.5-18mpg under same load. I didn't notice any different dic indication or lights on dash to tell me I was running on 4 cylinders or not. How is this? Did I accidently hit a button and find another highway gear? I read the manual when i got home to find out my truck has a auto fuel management system. How is this triggered? What do you all know about this? I really got good fuel econmy on the way home. More than I ever got since i owned this truck. How is this?

Diesels don't have the fuel management system.......

Maybe you have something wrong with your tach like I do, every so often. Doesn't explain fuel mileage though.......(see pics below)

What size tires are you running? Stock, which ones?

Im running 33" with a 4" lift but have corrected for tire sizing in the programmer.

First off i searched this forum for question or problems with Gm's active fuel management system to no discovery.

I 've owned my lmm for about 6 months now and have always ran about 80mph on the highway at 1800-1900 rpm's and getting about16mpg. This is of course empty with no towing.

Just yesturday I travelled from Baton Rouge and was running 80m.p.h. at 1200rpm's and improving to 17.5-18mpg under same load. I didn't notice any different dic indication or lights on dash to tell me I was running on 4 cylinders or not. How is this? Did I accidently hit a button and find another highway gear? I read the manual when i got home to find out my truck has a auto fuel management system. How is this triggered? What do you all know about this? I really got good fuel econmy on the way home. More than I ever got since i owned this truck. How is this?


guess my quess is how did you go faster with less rpms than before?? you either had one hella tail wind, you was drafting a big rig, or truck grew a new gear. :think:

No same speed just dropped about 600 rpm's like i shifted into a new gear or something.

No drafting

and yes just a breeze for a tailwind but I wouldn't think that would be good enough for a 600rpm drop in the engine.

I just think my truck finally shifted into a sixth gear, and thought this may have happened to some of you.

guess it was just your lucky day... mine wont get that kinda mpg running 55mph.. congrats on a wierd.. high fuel mileage truck though

...yeah I need to find that "gear"

Im normally running 1700 rpms @ 80 with 35s. If you was running 80 in 5th you'd be running around 2100. So 1800-1900 would be what you should be running. Wonder if some how your tire size got screwed up in your program causing you to be running slower than you thought you was and that would cause a increase in mileage.

Sounds to like you have the speedometer problem where you speed is shown inaccurately.

Please show what truck you have in your sig.