Crutchfield is saying I need the GMOS-01. They also have a PAC RP5-GM11 listed as well for the steering wheel control along with the Metra 95-3527 dash kit and a Metra 40-GM10 antenna adaptor. Sounds like I need both the GMOS and PAC harnesses for this install?
On edit, the Crutchfield chat advisor said I would only need the PAC RP5-GM11 and not the GMOS.