What modules will I need to install a D3 in my 2003 GMC Sierra with bose and steering wheel controls and still be able to use the steering wheel controls? Any sources to get them from?

You need the PAC Audio SWI-PS for the steering wheel controls. Not an easy unit to get to work correctly or long term.

For the Bose/Chime adapter, check out Metraonline.com...you're going to need a GMOS-LAN-XX unit, where XX is 01-04.

i would definitely go with a Metra wire harness, as i have had so many problems with many many Scosche modules

I just did a similar install using all PAC modules. You will need the steering wheel module, the chime module and the basic wiring harness module. Amazon had the best pricing on these a couple of weeks ago.