If the car is not under any kind of warranty, then you could find somebody that tunes PCM'*, and have them tune out the anti-theft altogether, I know a guy that you can mail your PCM, and he can flash it, then send it back to you, he normally charges around 100.00 for that, you pay shipping...
I'd get this bypass first, and give it a try.
GM VATS Bypass Module For LS1 and LT1 GM VATS Bypass Module For LS1 and LT1 [gmvats] - $24.95 : 3rdBrakeFlasher, E-commerce web site
I have not installed one myself yet, I just found the resistance of the pellet for my original key, I used a 1.00 radioshack resistor, and put it on the wire block near my left foot, where the wires from the key/ignition cylinder meet the wires coming from the TDM.
I'd suggest getting that module in the link above, it should not be hard to hook up yourself, I'll see if I can find something showing the location of your TDM, mine was behind my glove box..