It will make a difference, but how much is a hard to answer question. Most official testing is only with the most common installed equipment. So finding the difference relies on user reports.
Ford did test the new F150 with higher GVWR separately. I don't know the equipment differences, but it is a safe assumption the rear ends are different. It is a one to two MPG difference, with the bigger one going to the larger engine.
https://www.fueleconomy.gov/feg/Find...37051&id=37047
The Ram 1500 HFE will likely have the shortest rear end, and it does get a little better than the non high efficiency model. The HFE isn't available in 4WD for direct comparison though.
https://www.fueleconomy.gov/feg/Find...36545&id=36597
Using a gear calculator like this,
Gear Ratio Calculator, could shed better light by comparing the engine rpms at certain speeds.
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