Focus

Old barn wood. It's appropriate to not be in focus though since I am severely struggling with focus issues that I cannot seem to solve. If anyone can help I would greatly appreciate it. I shoot Nikon and over the summer started to realize that I had to throw out a large portion of images from a session due to them not being in focus. I thought it might be my old D300 camera so I've bought a brand new D700. That didn't fix it (and I am not impressed with the D700 by the way). I thought it was my 50mm not focusing correctly so I have sent it in for repair. This is a 50mm I rented for the day and I still had a lot of focus issues. Confused. I also had a shoot where I used my old zoom lens, which is hit or miss and mostly miss at the far end of its 28-105mm. At 105mm, chances are nothing is sharp. I am about at the breaking point and have no idea what to do to solve it. I put the focus point right on the damn center of the eyeball, I am not shooting wide open any more, and most of the shots are at a plenty high shutter speed and often the focus is not there even on a still subject, like a sleeping baby. Can anyone help?! I am getting tempted to just throw out all my gear and start over again. But what if it's me?!