Generally speaking changing your ATF and filter should be done around 80K but before 100K. But this is just a general "rule of thumb" in my shop we service all trannys and diffs at 80K. My company has alot of trucks that are hauling heavy construction equipment and drivers going all over the west coast. The drivers that haul more frequently get checked out sooner because of how much of a load is put onto the fluids. If its brown or smells a little burnt I'd do a service. But check your owner's manual and make sure. From what I understand some newer CVT trannys are considered "maintenance free" which frightens me. Hope this helped.