As
@Hall mentioned, the mileage between drain/fill depends on the model and usage. Vans/trucks seem to require more frequent replacement than cars, and towing or other severe conditions change things, too. For example, I tow frequently with my Odyssey, and DW1 didn't hold up very well in this situation (noticeable changes to the shift "feel" after a 1300 mile trip with a 17 ft boat). I switched to full synthetic ATF about 7 years ago to minimize this issue. So far, Pennzoil Platinum LV, Maxlife, and Amalie have all performed similarly, with somewhat better durability than DW1. I say "somewhat" because the shifts still get a little sloppy after towing, just not quite as bad as with DW1. Regardless, I do a single drain/fill each year (15k miles) to keep it fresh.