With the locker and it being a DD I would seriously only go with 4.56's with the 33's. For the on and offroad driving you do 4.88's is gonna be too steep IMO. Even when I do my SAS, SOA and 35's I'm only going upto 4.56's and I'll be doing more aggressive rock crawling/ trailin' then you do. In the end it's up to you but I think you'll put too much strain on the drivetrain parts.
The locker has nothing to do with it?
4.88's should be the minimum if you are eventually gonna run 35's (unless you plan on doing a V8 swap). With hardcore rock crawling 4.56's and 35's isn't what I'd run...the BW transfercases just don't have a low enough first 4wheel-Lo gear to run that ratio for me. I'd want a crawl ratio in the mid 50, but you may not even get low 40's with 35's/4.56's.
4.88's isnt gonna stress the drive train at all, its actually gonna make the motor work more efficiently and the tranny will also actually have
less strain on it that with 4.10's/4.56's. Try riding your bike up the hill in 3-3, legs tired? Now that's drivetrain strain, but the same person in 1-1 can climb the side of a mountain and not nearly be as wiped at the end of the day (you being the drivetrain). This only becomes a problem about 5.13 ratio gears, as the pinion is so small that there is a good change you can break it under the right circumstances. This isn't ever gonna happen with 4.88's and the 4.0L V6...
Plus, if he goes with 4.88's now, if he ever wants to go to 35's, he will be running the
perfect setup and won't have to change anything else. We all know it is inevitable and the next logical step. Why waste money on re-gearing twice when you can do it right the first time around?
With my setup I get good gas mileage, it wheels awesome, and drives like a dream. Win, win win. No drawbacks other than a lower cruising speed. I HIGHLY suggest it.