If the truck is still under warrenty, bring it to a dealer. The truck should open with both the remote & key. The only tthing is, when you lock it with the remote, you need to open it with the remote. Says so in your OM. If you use the key after locking it with the remote, the horn will start to go off. TRUST ME! I KNOW! It does on the Canadian models anyway.
Sounds to me like the guy never used the key any now the lock won't turn because its stiff and needs to be lubed. If he you have a problem with the locks on a new truck, wouldn't you bring it in and get checked. Hope you had the truck inspected