I know on my 2008 LGT I would need to tap two wires behind the speedometer/cluster. I am not sure if it is different for your model year. Also, did you see any of these threads? They helped me significantly with all of my navi and audio builds/mods:
I apologize if you already mentioned this, I only skimmed your threads on this subject. I have ordered harnesses from the last site and that guy is really amazing. Very helpful!