A couple of years ago I got a new camera body. I also started to get blurry shots about the same time. I thought it was the camera body. I tried my old body again, and realized that I can no longer shoot hand held as steady as I used to. After a lot of experimenting and missed photo ops, I ended up relearning a lot of what I thought I knew. It's all about technique. I shoot with a Manfrotto tripod and cheap Manfrotto ball head. I'd like to get a better tripod head, but there are things you can do...
Tie a rope or strap to the underside of the tripod mount. Pull it down with your foot when shooting to add a bit more stability. Avoid raising the center stalk if at all possible.
Do what john said, use mirror lockup. I'll add that with mirror lockup, you should use a remote shutter cable also. Mine is a cheap one from E-bay.
You'll have to experiment, but as Adam said, F/8 - F/11 are generally sweet spots for sharpness, especially APS-C size sensors. I can get some pretty sharp photos at f/7 (mine does 1/2 stops which is really handy).
There is a shortcut trick to focusing to infinity, AKA hyperfocal settings, that is to focus on a point 1/3 into the scene.