The D30 holds up fine to 35" tire and a locker, within reason. With upgraded alloy axle shafts, it will hold up to nearly anything you can throw at it so long as you stay with nothing bigger than 35" tires.
Regarding regearing from 4.56 to 4.88, that depends on your $$$ situation. You are already having to regear the rear axle. If another $500 or so to regear the front axle too is not a big deal, regearing both to 4.88 would be a very good thing to do. 4.88 with the 5-speed and 35" tires is the ideal ratio for both highway and offroad use. I had that combination for years and it was really sweet both on the highway and offroad. 4.56 "works" for 35" tires but 4.88 is a better all-around ratio for that large and heavy of a tire.