Don't. You're not going to improve anything, as we see.
ive done this with my pentax and ive done it with my canon, and ive never had such a fuzzy result.
The odds of anything being wrong with the camera are very low. The 50D is tack sharp stopped down, but an absolute mess wide open. If you want a reasonably sharp 50 wide open, you'll have to jump to the 50G.
As to autofocus, the standard wildlife shooter's settings work for just about everything:
AFC 9 points
Back button assigned to AF On Don't fight us on this, just do it. All Nikon cameras work better that way