I still think you should eliminate the possibility that you do have a problem with the lens or camera. Just use mirror lockup and a reasonably high shutter speed. And Dave's advice is good - maybe output a 1200 pixel wide jpeg and see if you can sharpen it up.
I won't join the chorus on technique other than to say that I relax, breathe out while I release the shutter and often take burts of two to four shots. It's surprising how often one turns out to be appreciably sharper than the others.