I too have several AF lens for my K-r. After a couple tests I decided I had a minor FF problem - follow these steps USING A TRIPOD...
#1- make sure your viewfinder's diopter adjustment is correct for your vision situation. Manually focus as best you can at a subject at infinity, then tweak your viewfinder using the little lever above the viewfinder for the sharpest image.
#2- Use auto-focus and compare how the AF functions show the viewfinder and liveview images. At infinity, there shouldn't be any difference (other than the reduced resolution of the LCD itself) ... If there is, we may be talking about a repair issue, not a simple FF or BF issue.
#3- Use auto-focus on an object just further than your close focus limit and repeat the steps in #2. No real difference?, no FF/BF. Small difference? Then you may need to use the built-in AF adjustment.
If you do need to make an adjustment, don't guess. Use a tool to accurately make your adjustments. You can buy the expensive tool or see
THIS THREAD. It takes longer to read the instructions than it does to actually make any needed adjustment.
For what it is worth, I set my 18-55 kit lens at the mid-point in its zoom range to make my adjustments. It was worked just fine across all my AF lens. Especially as I rarely shoot wide-open.