Have you considered having your oil analyzed? It might give you a better picture of what is going on inside your engine. I sent away to Blackstone Labs for a package on this, and they sent me a vial at no charge. Just drain some oil into the vial, send it to them, and they'll give you a report. I haven't done it yet, but plan to get to it fairly soon.

http://www.blackstone-labs.com/