Engine Dies In Anything But Park 4l80E

[Hambone!]

Got a good prob here if anyone can shed some light on it. Not really a Pro-Touring vehicle, but after reading several sites, you guys are much more technical than the truck forums. Have a 2000 Sierra with a supercharged LS3 (Thx to Travis) and a 4L80E trans. Starts and revs ok, but ign goes away as soon as I take it out of Park. Rev it up, shift, slam it back into Park, and the engine will catch itself and run. Occasionally the shift indicator shows "2", mostly it follows the position of the shifter. My scanner also shows the feedback from the trans, and while the shifter is in Park, the trans reports "2".....sometimes "1" when revved in Park. Nothing else happens, no loading of the engine, no noises, clunks, vibrations...nothing. The PRNDL switch is new, which incorporates the Neutral Safety switch. Any ideas?