Ok, so I have a Civic wagon with 30" mud tires on it. I am running the stock D16a6/ 6 speed and it's fine around town, but will not pull 5th gear on the highway. Also I need to be able to go slower in the super low gear for rock crawling, hill climbs, etc. I am considering having custom gears made for it since there is nothing out there that will do what I need. I need some basic understanding of the layout of the AWD transmission. How is the propeller shaft connected? Will it change speed in relation to the final drive gear ratio? Any input is appreciated.

 

The super low gear is tiny. I don't recommend using it in any instance that is going to put a significant load on it. The driveshaft is engaged in the transfer case via a selector sleeve, just like standard manual forward gears are. If you want to change the rear end gearing you will also need to change the transfer gear to match. Custom gears are certainly doable, but just a pair of shaft mounted gears (i.e. 3rd gear, not 1st, 2nd or FD) are $1,000+.