Axle gears really have more to do with setting cruising RPM than offroad performance. Consider the actual numbers
3 speed x dana 20(t-shift) x axle ratio = compound low
2.99 x 2.46 x 4.56 = 33.54
Now lets say you go ahead a spend a bunch of money and gear it at 5.13.
2.99 x 2.46 x 5.13 = 37.73
Lets say you get crazy and drop in a 4:1 atlas transfercase
2.99 x 4 x 4.56 = 54.54
Ok, that's getting better. But you've still got some cash burning a hole in your pocket, so you gear it out at 5.13 too.
2.99 x 4 x 5.13 = 61.35
Now looks what happens if you drop in a ZF.
5.72 x 2.46 x 4.56 = 64.16
Not bad at all. But you say you'll primarily be on the trail, so you really don't care about that ZF Overdrive. How about an NP435?
6.69 x 2.46 x 4.56 = 75.05
See where your problem is?
The NP435 or even T-18 are very cheap ways to get great bulletproof gearing. You can pick these transmissions up for $50-200. Other than some tunnel mods, they pretty much bolt right up with a transfercase adapter. No driveline mods required.
I run the NP435 and 4.56's with 36's and I'm very happy with that combination.
