I travel every weekend with mine. I found that #3 is about the best. I do highway and intown driving on the same trip every weekend. I have got as high as 21.4 mpg and as low as 18 mpg. It depends on traffic and how many times you can't resist the feeling of POWER! I stay away from the higher settings only because Edge suggests it except for short periods of time. Some of the guys, I see, do go higher and may be on to something. A higher setting used moderately may be OK, but I don't have that experience. I wouldn't doubt what they say, since they have done it. I have not made any modifications to the tranny and don't want to put it in limp mode. Besides, I can't imagine getting any better than 21.4. That trip was considerably moderate driving and hard to do.
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HAD - 94 Chevy Dually 4x4 - 6.5 Turbo
96 Chevy Ext.cab 4x4 - 6.5 Turbo
99 GMC Dually 4x4 - 6.5 Turbo
HAVE - 2005 GMC Sierra crew/6'box - 4X4 - Duramax w/Allison. Fully loaded - AiRaid intake - 4" Pinnicle Performance Exhaust (No Converter - Straight through muffler) - EGR blocker plate - Edge Juice w/attitude - 2" plug in Turbo Resinator -