Fuel mileage question.

And here is another question, would i be Better off running 37 inch tires or 35s? I would think 37s would bring my rpms down and effectively bring my 4.10 gears closer to 3.73s I'll have to check the calipers for resistance if there is just grease them or I should replace the pins or the whole assembly? And again how do I check the rear tires with a limited slip diff pull the axle shaft out I guess? I just tried switching back to the stock tune with dpf delete if the lie o meter is acuracte without the tune than I should be at 13 city and haven't driven on the highway yet so that would already be an improvement.. Last tank consisting of 3/4 tank at 75-78mph and last quarter city calculated to be 11.9 347 Miles (times1.12 for actual mileage with 35s equals 388 with 32.6 gal of fuel not very good for mostly highway driving...

Well the front right seems like it maybe frozen it doesn't roll after I'm done rolling it. It stops pretty fast and the front left rolls for a second not flvery long tho and still not sure how I will check the back.
And the stock size is suppose to be 245 75 17 which is 31.5 and I cruelty have 35s so 31.5x3.14 equals 98.9 and 35 x3.14 equals 109.9 109.9/98.9 equals 1.11 so I need to multiply my mileage by 1.11 and I figured the lie ometer thing out but it could say I'm getting 15 and I'll be getting 10.5 or it can say 18 and I'm getting 11.5 but I can never seem to get over 18...
And yes you are right that there is more weight but weight will only factor in city if you never stop the only thing that will affect mpg will be resistance be it rolling or wind so yes I may get a touch more resistance from 1 inch of tire but the weight will not negatively affect my mpg on the freeway so it will hopefully act at 373 gears instead of 390 ish with my tires now

Never thought of getting the new tunes for that, are you speaking from experience or what you've heard? And I have 35x12.5 20s I never said 315 70 17s even if they were 34.7 how either way you look at it 9% vs 11 I calculated....so it's even lower than we expected! ? lol And that 3 percent difference only accounts for 1/3 mile per gallon when I'm getting 11 that's a very small percentage. You would be right about the added wind resistance. I mean yes I understand I'm not going to get 20 mpg but I would hope to get better than a stock 6.4 when mine is deleted and tuned. Stock I've heard of 15-16 if it's not going through regen all the time and with regen it's still getting 10 -11 same as mine except I'm not dumping fuel out like a stock truck I would just love to figure out what's accounts for the other % lost in fuel economy does anyone else's front Huns get too hot to touch with highway driving I'm wondering if that could be a cause. They were pretty hot last long trip I took but maybe it's normal brake heat? Thanks for the ideas tho guys keep el coming!