I've seen this banter a bit, and it's always a question posed along the lines of "T-case OR diffs?".
Well, the best answer is, both. But that'$ not alway$ the an$wer folk$ are $seeking.
Diff gears aren't cheap, unless you have a good line on some, like used or from a yard. Set up, if you don't know how or have a buddy, can be pricey. If done wrong, you can toast your pricey gears quickly. And the taller your gear, like the Kick ones, the less course the grind gets. All gears are a compromise between strength and noise.
Tall Kick gears (5.12s and 5.62s) and hush-hush quite, but that's because of a more smooth grind.
When I say grind, I'm talking tooth count and pitch. This is important when choosing a gear as you can tell there is many ratios very close to each other, say 4.57, 4.62, or 5.12, 5.38 and 5.43, or 5.62 and 5.83 (5.62 very weak, 5.83 very strong).
With that aside, T-case reduction is the ONLY way to reach crawler speed. But, in doing so, increases force on the pinion, which any D30 owner will tell you isn't all that cool. Tiny pinion, like what the Zook has, don't hold up well to added torque. But, the sammy's saving grace is low HP and light weight, which make for a long life with a moderate foot.
I've run the 4.16 case and Kick 5.12s with 33's for a few years now, and you know I would rather idle and crawl and throttle-monger. No problems. But wanting to go deeper (and idle and crawl), I will have an effective ratio out of the t-case of 9.30 to one, and but high range will not be reduced the 18.3%, as that is based on the Sammy tranny, which spins for 3.73's. I'm adding the Kick auto, which spins for 4.62's. Then I also have to add in the torque converter, which will increase the effective ratio again. Oh yeah, then figure in that the tires will increase from 33" to 35".
What's this all mean? Well, a headache when you crunch the numbers over and over for one.
But for me, it means I still need a R&P swap if I want my high range to be somewhere in the ballpark, and it has to be higher than the 4.62 ratio that the auto normally spins. So, as I do my math (which isn't so hot as I did got to a public school), would be in the high 4:1s. But that's not my real concern. The weenie pinion gear, along with a 9+:1 on low range AND torque converter and bigass rubber, is my real concern.
The 4.88's I have from my GV are far stronger than that Kicks 4.62 and 5.12s, and they had to be. V6 power and more weight dictated a stronger grind. Bonus, I have a set when I swapped up to 5.12's in my GV. And don't go there, as I've learned alot about R&P strength since. You know, a good friend named Steve, who really does know a lot about Zooks, tried to teach me about gear grinds and the right way to do it, but I was on my "purist" trip and didn't listen. To sum it up, I've wasted about $1800 in GV drivetrain by NOT listening to him.
<=what should be done to me
So, for you, now, a gear set should be just fine. Heck, you can pull off 32"-33" tires with just the 5.14s, something that used to require t-case gears. With finese rather than force, you should be fine. Remember, the 3.73 is one helluva strong gear. But bulletproof everything else in the drivetrain. When you got time and money, scrounge up a set of 4.10's, or better, 4.30's from a manual GV as they don't need cans and spacers, and that should make the truck more peppy and better gears, taking some of the load off the pinion.
That help any, or make you as confused as me?