A prmossory note is a promise to pay money. A perfected secured interest in a piece of property requires what's called a UCC filing, so your DIY document may not be enforceable anyway.
The statute of limitations runs from the date of breach, not the date of the document or oral agreement.
KY has very long deadlines, 15 years from the date of breach, to sue on a written contract or promissory note.
Stop doing your own legal work --see a business litigator for accurate help.
PLEASE READ THIS BEFORE YOU COMMENT, EMAIL ME OR PHONE ME. I'm only licensed in CA. This answer doesn't make me your lawyer, and neither do follow-up comments and/or emails and/or phone calls, and you shouldn't expect me to respond to your further questions if you haven't hired me. We need an actual agreement confirmed in writing before any attorney-client relationship is formed. This answer doesn't constitute legal advice, and shouldn't be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue.
It does not appear that you have a perfected security interest in the truck. But that doesn't mean that the promissory note isn't enforceable. While you may, indeed, need to stop doing your own legal work, in many states small claims courts are an accessible, affordable way to collect on debts like this. You don't report how much the promissory notes were for, but if they're less than $1,500 each, you may be able to go to small claims court. The KY Attorney General has a guide for small claims available here: http://courts.ky.gov/nr/rdonlyres/e452ffe9-4aa1-4879-b459-64ffbd3ab5bb/0/p6smallclaimshandbook310web.pdf
If the amounts of the notes are substantially greater than $1,500 or if you don't understand the small claims process, you may need to retain an attorney. At any rate, it may be worth your time to consult with an attorney for an hour, just to get his/her take on your situation.
Licensed in Washington. This is NOT legal advice and you would be foolish to rely upon it, so don't. The information is for general educational purposes. State laws vary and the specific facts of any situation are unique; a tiny detail may have a huge impact on your legal situation. If you have a legal problem, talk to an attorney licensed in your state. My answer does not create an attorney-client relationship.