The PIM is a small box on LSx vehicles that retained the ALDL BCM and bus but where the PCM only spoke OBD2. So this little box does the conversion between the two interface types. Will update this thread with more info later, but for now here are some pics of it...
PIM: Powertrain Interface Module
Re: PIM: Powertrain Interface Module
Sounds like you could make a vpw to ttl convertor and flash the pcm with it.Might have to get one and have a try. 
