If your stepping up to 34/35 inch tires I wouldn't go up more than 4.30s and you could run 70 mph with the stock 4.88's at 2400.
Might want to try it with the new tires before jumping into a gear swap.
I went from a big tired F-350 single to a dually for the side sway stability.
300 lbs isn't going to make much difference in fuel savings on a truck that weighs around 9500 lbs empty.
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Mine: 04 F-450 sc 4x4 fb drw 5.9 12v 215 ppump, zf6, kdp fixed, 3k gsk, AFC Live, super b single, pusher intake, d-celerator ebrake
Hers:2018 F-150 sc 4x4 5.0
Farm trucks: 01 Z71 ext cab, 95 S10, 93 F-800 8.3 Cummins, 87 AM General 5 ton
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