First off here is the manual for the special additions:
http://www.gmfleet.com/content/dam/...Shared_Resources/PDFs/2012_Tahoe_PPV_ 5W4.pdf
Second, do NOT let the manual fool you it states that the dash wiring pigtail comes out behind the grille, IT DOES NOT! The front wiring terminal is behind the brake master cylinder.
Third the BEST thing I did to my truck was to add insulation (aluminized bubble wrap) above the headliner, the difference was incredible. This means you have to drop the headliner, which is the best decision for multiple antenna installation.
This brings me to the part that will spark debates in an empty radio shack. Antenna location: I have lots of problems with front end overload on my scanner whenever anything VHF keys up in my truck, UHF - not so much. I have also noted a decrease in overall sensitivity on my scanner in the VHF mode over the years as well. This is all anecdotal on my part but if at all possible I would locate the 2 Meter and the powerhouse Kenwood antennas as far from the scanner antenna as possible.
We are anxiously awaiting some pics of your new delivery!!