The Tetrix gearbox can be easily changed from 52:1 (as received) to either 31.2:1 or10.4:1.
When you take off the gearbox end plate by carefully grinding, using a dremel, the 3 tabs you will notice 3 compound gear sets each on a separate shaft. 2 are identical.
If you connect (stack) the 2 identical gearsets by lets say by soldering them you will find that by some axial endplay adjustement these will fit nicely and you will have a 31.2:1 gearbox. You may need to push the motor drive gear onto the motor shaft and even grind down its length a little bit.
To get a 10.4:1 reduction stack and attach one of the intermediate gearsets with the input and with even less axial adjustment you will have a 10.4:1 reduction.
The motors can drive a 4 inch wheel with 31.2:1 reduction and with light enough bot you can climb in ~ 2.5 seconds.
I calculate that with 10.4:1 and 2 inch wheels you can climb under 2 seconds.