I too own a 1996 Monte Carlo Z34 and I have done a lot of recent research on it. One of the interesting things I discovered related to the PCM. It seems to have "logic" problems with the sensors. Where as a sensor can send just one intermittent signal and the PMC's logic thinks it's a continuous problem. So, I started researching another brand of PCM, and found this.
http://www.autoanything.com/performa...0A2601749.aspx
It's a High Performance PCM made by Jet Performance Products. I plan on getting one as soon as my funds will allow. I am also going to invest in a ODB II scan tool, not the one's sold at autoparts stores, although they may be fine, I found one I can hook up to my laptop which will give me the exact same capabilities and read outs that any dealer can do at the same cost as the autoparts version
http://www.obdpros.com/product_info.php?products_id=133
Now with this diagnostics aresonal and a far improved PCM and regular maintenance I hope to avoid or at least decrease the horror stories I am reading in this thread. My biggest fear now is replacing the timing belt on the DOHC Interferace type monster. :o)