New tires and MPG

[Cupped_up]

Before you say it... no I didn’t purchase my truck for MPGs. BUT, it would be nice to keep the few I have so I’m getting some research before I pull the trigger.
I ordered the ORG on my CC 6’4 bed and am thinking about either 275/70r18 or 275/65r20 in an AT tire. I know bigger/heavier means less MPG, but here’s what I’m looking at...

275/70r18 Toyo AT3 - - 33” - - 50lbs
275/65r20 Toyo AT3 - - 34” - - 54lbs

the stock ORG tires are 49lbs, so I’d be going up only 1 or 2 inches and only 1lb and 5 lbs per tire. Will keeping the weight down on each tire keep the mileage better even though I’m going up in size?

 

[ElkoNV]

I am buying my truck for MPG's I have 3.92 gears and going with Nitto Grappler G2 275/65R20 116S they are 47#'s. The two things that contribute a lot to fuel economy gain or loss are weight and contact patch (width). With the Ecodiesel I knew I was going to put on larger tires so I went with 3.92 to keep the gearing in a range to handle it. A few ecodiesel guys have reported an increase in milage, only 1-2 mpg's with this tire but much better than a hit and why I am having it put on. If you have 275's now and stay with the same width and very close to weight any hit should be negligible. The next milage hit comes from rolling resistance, more aggressive tread less economy, MT's are always worse than AT's are always worse than Summer, how much is tire specific.

 

[Cupped_up]

I have the 5.7, non-etorque, 3.21 gearing. I know the 3.92 would be better for larger heavier tires but the two tires I’m looking at are only one or five pounds heavier, same width.