The controller is very simple, so has very little to do with anything other than switching one of the radios into repeat. The lack of distance has nothing to do with the controller, so you won’t find problems or help targeted at it. Googling the Gam3Gear product won’t reveal much at all. Are you trying in band, or out - that is the critical issue for success? If you are willing to open up the radios, you can get a much better system by simply using a squelch open tap (one that goes up to 5V or power supply rail when the squelch activates - then use this to trigger transmit on the other unit with a small logic circuit.
So - can you confirm the problem is with cross band use (when there could be a solution) or in band, where with less selective radios, there really may not be without adding filters.