I had an 00 lightning that did not have the keypad. All the wiring was there for it. I bought a pad and a handle that had the opening for the pad.
I put it together, walked into the parts department at my local dealer and they looked it up. I think it's odd that they are trying to get you to come in (other than seeing it's your truck). Try calling until you get someone different. Or go in and make sure they're not trying to charge you for this service.