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There is a post of someone here on this board that refinanced with their own lender for a lower rate - but that is the first time I have ever heard of it. Most lenders want to keep their contracts in place and are not out to save you money. Unless they can take you from a different lender...then that is a different story!
Chase offered to refinance my auto loan that was thru them. I chose PenFed instead because they offered a much better rate at the time.