The only ratio I understand is the 4:1 transfer case in Rubi's and the 2.72:1 for the rest of us. Folks here are multiplying tranny ratio -times- transfer case ratio -times- axle ratio -times-? But as I see this, it doesn't double everything does it? Where it's located, it can only affect the transmission gearing while all else stays the same, right? As such it's not going to slow down the JK to 3 feet per minute at 4000 RPM, right? It seems to me it's going to give those of us who are Rubically challenged a nice way to deal with those steep descents that make us X and Saraha owners have to over use our brakes. Please forgive my lack of intelligence here.
Yes you will get better engine braking, but more importantly the crawl ratio will go way up. This gives you more control and makes climbing rocks much easier, and also allows for higher rpm at slower speeds, so you have more power going to the wheels. For crawling, automatics generally don't need as high a crawl ratio as manuals, due to the multiplication of the torque converter, which roughly is 2:1, so an automatic with a 75:1 crawl ratio will "crawl" more like a manual with 150:1.