It is my experience that the axel is just not strong enough to handle duals. As far as changing final drives I am looking into New Holland final drives for mine , but am not sure if they will pan out. There is nothing that I know of that is a easy fix for the weak axels. If you have not had troubles with your setup you might want to think about axel spacers to get your spaceing right. One of my 8590's has them and they seem to be a good alternative. They correct the spaceing problem, without adding more stress on the axels, by moving the final drives out, not the wheels.