Did GM actually offer an upgrade to add a lock to the tailgate for these years? I have dug through several threads and have receive conflicting information mainly due to the split year of the 07 trucks and confusion at that time between NBS and NNBS. I found one part number referenced for 03-06 but with not picture being available I don't want to purchase it only to find out it is the wrong one. I know bully and pop n lock offer alternatives but they appear to have mixed reviews. Thanks in advance.