I bought the D3 and the XM tuner. Do i install both antennas from the D3 and the XM tuner, just the one on D3 unit, or just the one on the XM tuner? Thanks a lot for all the responses. This forum is great.

You have to install both. The one from the D3 is the antenna for the GPS navigation. The one for the XM tuner is for XM. Two different systems, 2 different antennas. Oh, and hook up the radio antenna as well... lol