Either a PAC RP5-GM11 or an Access GMOS-4 with the ASWC-1 will be what you want, if you want to keep the amp and have sterring wheel controls. If you want to bypass the amp the Axxess AX-GMCL2-SWC will work for you. It will allow you to still run the amp or bypass it as well as retain the steering wheel controls.
@Ziggina02tb I have an Axxess GMOS-4 set a side from a previous install if your interested. I removed it from my install because I had a bad humming sound coming from my speakers, turns out it was a bad set of rca's that caused it and Not the GMOS-4 adapter. It was an expensive dumb move on my part for not checking the rca's and since the rp5-gm11 is like $130 bucks at the time.
I'll take $35 for the unit and you have to cover shipping which would be around $7-$8 for flat rate usps box in and around the US. If he passes on this deal and if anyone else is interested just send me a pm.