I let the oil monitor judge my oil changes. They have been 7-9k with Mobil 1 or Castrol Syntec synthetics. When I use dino oil, i go 3k like clockwork. I dump my truck tranny fluid and filter every 30K, and at that mileage it looks like thats a good thing.But it hauls a 8600lb boat. I plan to do the GXP @ 50K. I have regularly change my antifreeze every 3 years on all my vehicles. The GXP is getting a good flush and change this spring, it'* an '05 but bought new in '06.