Mike,
I don't have your exact lens, but I do have a Tokina 80-200/2.8 ATX-Pro that basically does the same thing. On an autofocus film camera (Z-1, PZ-1P, MZ-S) it is sharp as a tack and nails focus almost every time, but on my K10 & K20, 9 out of 10 shots come out blurry. I checked the focus alignment and on both cameras and it was back focusing pretty bad (more so on the K20 than the K10) but on the K20 I could adjust the focus. Even with the focus adjusted and the focus point locked in on the middle point, it still misses focus 25% of the time. I sent it into to Tokina several years ago and they told me that the lens was fine, it was just designed for film cameras, not digital. That may be the case, but I own quite a few 'film' lenses and that is the only lens that focuses that bad on digital. Another issue could be that the focus system on the K10 and K20 is not the best in the world (my PZ cameras focus faster and more accurately and they are nearly 20 years old with a supposedly inferior focus system) I have heard from a friend that the 80-200 focuses much better on the K3 due to a much improved focus system, so hopefully my issue will be resolved here in about another month.
BTW a quick way to check to see if it is the focus point or just a blurry lens or faulty camera is to take a news paper and lay it on the floor or a table. With your camera preferably on a tripod (but you could do it hand held) aim at the newspaper from about a 45 degree (or less) angle. Focus on a set point around the middle of the paper and shoot. Look at the resulting photo, if nothing is in focus I would guess that there is something either wrong with the focus system on your camera or the lens itself. If any part of the paper IS in focus then this will show where your lens is focusing in relation to where the focus system is aimed at.
Good luck,
Steve