If the effective ratio is the same, what else is there to overcome?

1) The additional inertia of the heavier tires/wheels

2) Maybe a very small different coefficient of friction -- tire to road friction is small, because it's roughly the same weight vehicle on a bigger tire contact patch (less friction over a bigger area), plus probably a little more internal friction in a bigger piece of rubber, but that can't amount to much.

What am I missing?

90 LWB Montero, 270k, 265/75R16, 16x8 ARE Bajas, Budget Lift, Towbar, Aux Brakes (towed with camper), Jotto Desk, remote oil filter
92 bone stock base model beater
Parting out 4 more