No, this is at the primary drive (clutch) and reduces everything. The OP asked about regaining top speed with bigger tires so he would need to reduce high to do that.Is this a sub trans IGR that reduces low and reverse only? Do you know of a way to communicate with RBE other than Facebook?
As far as the sub-trans reduction, I have been watching another forum and the guy has been waiting months for parts from the Morris brothers. They are having some sort of "supply issues". The guy grenaded his sub-trans and had to cobble it together to get back on the trail. He only has high gear and still waiting for his parts from Zach. As you stated in another thread, you refuse to do business with the Morris brothers and now I see why