Possibly, but we have no information here to make a determination. It is never wise to enter into oral agreement. Although they are legal, they are also very difficult to prove. You could sue and then he could just say that the term of the lease was up and he took the truck. Speak to an attorney in your area for a 2nd opinion.
You need a lawyer for this one. Verbal agreements are notoriously difficult to enforce, largely because they're "he said, he said." I don't know what you think your understanding was, so I can't tell if it would be enforceable even if you could prove it.
Consult a commercial lawyer.
I am an attorney admitted solely in NY. None of the answers I submit on this forum constitutes legal advice, even to questioners in NY, and no attorney-client relationship is hereby created.