Just returned from dealership, was told I need a Vehicle Communication Interface Module for my 2014 Silverado 1500 in order for my on board Navigation/OnStar to work?? My question is can I purchase this unit myself or do I need the dealership, not a cheap option and I'm rather disappointed cause I bought this truck used with the hopes of using such an option and now its worthless ?? Any advise or suggestions are greatly appreciated and I might add I just joined so I'm a newbie !!?? Thanks