What tranny?
If you are running a compound t18 or Np435 getting a klune or doubler is silly. If you are running an automatic, Klune and doublers are silly.

Look at the #s, t18 or 435...6.69x2.0x4.88 = 65:1 not bad maybe upgrading to a m300 t-case... at 2.62 = 85.54:1 way coolcrawl ratio. If you pony up to a 3.8 atlas...but go down to 4.10 axle gears...104:1 almost too slow for v8 rockcrawling. I ran a 82:1 set up with my 35" BFGs for years and loved that ratio for pretty extreme trails.
That was 304 Amc, np435,m300 and 4.56 gears.
THis set up was great because the 1st gear ratio would almost climb anything without touching the gas. But when wheel speed was needed 2nd gear was not SOOOO low that I could quickly get the tires spinning for momentum trail obstacles.

Now I run automatics and I'll never go back, the ratio does not have to be so steep because the torque converter multiplies torque. So take, 2.7:1 Common 1st gear in a TH350 or 400 x 2.62x 4.88 =35:1 combine this with a v8 and you have perfection for a 35/36" tall tire.
My new buggy has 38" tires so I'm running 5.13 gears.
The cool part about a slush box is the the wide wheel speed to engine rpm and torque ratio.
You can climb a rock obstacle in 1st gear and stop in the middle and start again without loosing any torque transfer, also if you need wheel speed a quick throttle stab and you can get the tires whipping ALL in 1st gear.

However, with an auto, if you get a 4.0 t-case kit or an 4.3 atlas, combined with 4.88...56:1 is so low (for a v8) that you can't get the tires spinning without hitting 6k rpm. Unless you have a full manual valve body (which I do NOT recomend).

I have built, driven many combos on many trails/type around the country, let me know what you think and what you plan to do. I can help.

SD
Josh