I live on a hilly island and when coasting and driving normal with it on I was getting close to 8 mpg on average before my tuner and turning my mds off driving normal. After turning it off and with my fuel Econ set on my bully dog I am getting 13 now. Calculated after each fill up

 

Mds on*

 

I hate to say this, but if you are only getting 8 mpg there is definately something wrong with your truck. I have never seen an average lower than what you state is your top mpg 13, on my truck...never and I live in Tennessee where I can guarantee the hills are much larger than they are on Guam. I average from 15 to 17 for the last 6 years. Try turning the mds back on and drive sanely for a tank and report back on the result. I have a feeling you will see about the same result as you are getting now. Thank you for your service. Take care

 

Thanks . Befor I shipped here I lived in Texas and I was averaging 13 to 22 when I had 27560r20 driving city and highway but since I put 361350r17 it dramatically went Down from 8 to 10 mostly 8 tho

 

Also reasoning behind my mpg is the speed limit on Guam is 35 everywhere and the island is 26 miles long with terrible traffic

 

It looks like the tire size is eating your gas up. Going from a 32 inch tall tire to a 36 inch tall tire without a gear change is probably lugging your truck to death. You probably need 4.56 gears now to just get your gearing back to where it used to be, which will also get your mileage back. Had you said something about the tire change in the first place we would have seen why your mileage was varying so much. Try running your truck in 2nd gear for a while, since your speed limit is so low, that might just get you a little better mileage, or if the revs are too high, in second, turn off the overdrive. At 35 mph you certainly dont need overdrive or mds kicking in. Take care and let us know how it works out

 

Tex....I checked mine yesterday since I have the 20 inch tires like you used to have, and in 2nd gear at 35 mph I was around 2300 rpm with 3.92 gears so with your 36 inch tires, you should easily be able to run 2nd gear all day long at 35 mph, and probably still be slightly under 2000 rpm

 

Ill try this out. Thanks old man

 

I have 3.92 gears and 20 inch wheels with stock tires, at 35mph I'm right around 1650rpm give or take... but that's with the 5speed auto transmission.

Everyone ends up paying the price for bigger tires in some way shape or form.... Did you already reprogram the speedometer to compensate for the tire size change?

 

Yea I have fixed it with my bullydog gt