Don't these newer tractors made in the last several years have egr systems on them? If so I wouldn't be trying to stretch oil change intervals at all. Egr makes an engine really nasty on the inside.

With that said our newest engine on the farm is a '99, and i still change at 100 hours. I know that is overkill.

For those of you doing extended drain intervals I would strongly suggest sampling your oil and sending of to a lab to be anyalized. That way you know for sure you're doing the right thing.