30weight oil for the front diff. Most people get by fine with ATF of your choice. or you can use amsoils's reccomended fluid
In the transmission I'd run the Amsoil reccomended fluid. I have one out of 3 rangers that has never had a transmission fail, and it's the only one that's got amsoil fluid in the transmission. Not sure if it's coincidence, or just better oil, but the two rangers that are running polaris oil are both on their 3rd transmission.
I've run their 0w-40 powersports motor oil for about 2 years now, and I've had very good success with it. I also run the wix filter for the ranger, purchase it though amsoil's site. I buy a case at a time... Doing it that way I save about $15 per oil change over buying polaris oil/filter.
Their grease is great too.!
In the rear diff you should run 80/90w gear oil and you should be good to go.
Good luck with it!