The results are in, and the results are...my K100D body might actually be back focusing slightly!
I tested the Tamron using a PDF chart I got from the forums. I forgot the link, but it had the chart with millimeter graduations and required that I take photos focused on the center black bar at a 45 degree angle.
Anyway, it seems to be back-focusing, but I decided to do the same test with my Pentax 16-40 f4 just in case. I got the same results with both lenses, the sharpest focus seemed to be a little bit behind where it was suppose to be. I figure that the odds that both lenses are at fault is probably low, so my K100D body is more likely at fault.
I'm a little bummed, but not terribly since I don't really rely on such narrow depth of field which is why I never noticed this before. I'm gonna try to ring up the warranty with Pentax in a few weeks since I need my camera for the next several weekends. I won't be needing such narrow depth of field in my next photo ops, so the slight back focusing won't affect me.
I'll try to post some photos of the tests later, and test other aspects of the Tamron over the weekend. So far, the Tamron seems to be fine