I just installed a new Pioneer HU with the PAC RP5-GM11 into my 2004 Comp G a few days ago. Install was very simple, I was able to retain my steering controls but the buttons didnt match with what was programmed on the PAC. I had to reprogram it which was easy to do but still not a perfect match to my steering wheel controls but I can live with that. Some HU's will match better than others.
I have not had any problems with it other than that and losing the Date/Time on the DIC.