Can I still register my Gradient to get the ten year parts warranty?

Only if it was installed within the last sixty days. Gradient’s policy extends the five year parts coverage by another five years if the product is registered “within SIXTY (60) DAYS from the Original Date of Installation”. After that the window has closed, and any company offering to register a two year old unit and get you ten years of parts coverage is promising something the contract does not support. Registration is free, through the product registration page on gradientthermal.com. Note their shortcut link currently returns a 404.