ah, i get it. so basically, you just want to build a freeway flyer that hauls balls and clips 1800 rpm so it doesn't feel like it's revving it's tits off, and gets "reasonable" mileage.
reasonable in quotes in terms of acceptable for a 650hp motor.
so not knowing what speeds you travel at, i can't give you more than a guess based on the tire size and OD and say that i wouldn't run anything
less than a 3.70 gear. but having some experience with the 5.7 G3 in my ram, i can tell you it was most happy in the 1800~2000 range; which sat me between 65~75mph, and anything over that mileage decreased
rapidly, anything under that i had to get on the pedal to make the power available.
i understand that's not an apples to apples comparison, but it might give you at least sort of a starting point. the benefit here is that you've got gobs of power so you're not going to be wanting in that department no matter what gear ratio you pick.
here's a link to a gearing calculator that may be of some assistance:
[URL]https://spicerparts.com/calculators/transmission-ratio-rpm-calculator[/URL]