Well, I'm looking at my lens now, and I took it off the camera. The lens mount was loose, I turned the camera about 45 degrees, it held and clicked, as it turned it to 90 degrees to release it. All four screws on the mount are ready to come out and I'm just wondering if this is because at football and soccer I don't pick it up and put it down so much, but at golf I'm putting it into a cart and taking off all the time.
I do NOT have a tool right now to tighten those screws, as luck would have it. Also not claiming this is the issue.
Do not remount the lens until those screws are tightened!!!!!
I had a similar issue with a 70-200 f2.8 IS on a 1D, one of the mount screws came loose and jammed in the body mount recess. They were stuck together and it was only because I was working with a micre electrical engineer and he had some very cool small tools that he was able to separate the pair.
That is almost certainly your de-centering issue too.