Tunes: I don't think 800 - 1,000 is anywhere near the max. I put 1200 hours on an F250 and it was flawless the entire time. A commercial guy I spoke with said he changes them at 3,000 hours. Of course, he puts those hours on in about two year's time. If it takes five or ten years to collect those same hours, then you're more likely to see the other issues that Doc mentioned.