RichZ,
One test I always make during my preseason shake down, is to rotate the blower impeller by hand (while not connected to the tractor). If your hand cannot easily rotate all the parts, then there is a problem. Look for hay and other grasses.
Another test is to try and rotate the auger rakes while the shearpins are removed.
After reading all the posts, I suspect the rake(s) won't move by hand. For the shearpin to break, the power shaft will rotate but the auger rake won't. Look for grass or a missing bearing spacer at the end of the auger rake tube. IMHO, something very strong is holding that auger.