No. Deleting the file (there was only one) in the DCBackup folder didn't fix the problem. The horse gains skill in jumping (which is currently below 5), but racing is stuck at level 5. The rider gains skill in racing, the horse skill gain is static, stuck just below the threshold to reach level 6.
There's a worldcache folder, does it hurt anything to delete those files? There's two hidden springs files in there, which was the world containing the (now uninstalled) fountain of youth. Never mind, I found a post in the technical help thread which said it was OK to delete the files in this folder, so I did. It's still stuck.
So far, I've uninstalled the ubertoilet, fountain of youth, spell book... deleted the cache.package files and restarted the PC. (I don't recall buying windchimes, I couldn't find them in the installed objects so I can't uninstall them)
Racing skill gain still stuck. Any more ideas? I appreciate the help.
(On the bright side, the rider has gone from level 6 to level 8 riding skill during all this troubleshoot/test to see if it worked routine.)