Resilient channel will definitely help. It will decouple the drywall from the existing garage structure, creating a 2-leaf setup. Ideally, use 2 layers of drywall with greenglue between, mounted to the channel as described in Rod's book. Use insulation between the drywall and the existing studs of the garage. Seal everything up airtight and you'll have decent performance.
Dietrich Deluxe resilient channel has been getting lots of good hype lately, though I've never worked with it myself.
For even better performance, use RSIC clips with hat channel, as Rod shows in his book.