4x4 issue

So I baught this wheeler and never been able to figure out why the 4x4 is only engaging on left side but only in low gear. The right side simply doesn’t work at all it seems to me there might be a couple things wrong. I have put new bearings and seals in both hubs, new hub oil, and the washers...

I have a 06 sportsman 500 ho and runs great all summer long but when it comes time to plow it will not engage 4x4. It seems like if it's cold it won't shift in four wheel. Warm no problem at all in and out of four wheel on demand with switch as it should. What should o do or look for?