Well, if anything, this just proves how amazingly robust Flashhack is; had you attempted to flash this PCM using TunerCats, you would absolutely have had a brick on your hands.

Something is really wrong with your serial interface; even more wrong than the one on my '94 Corvette (the cause of which I have yet to determine).

The problem has nothing to do with the PCM having never been flashed before. That is completely irrelevant. The wiring would be the first suspect. Make sure that the grounds between the PCM and the ALDL connector are solid. Make sure the connections between the ALDL pins on the PCM and the bus connector are also solid. After that...you'll probably need something like an oscilloscope or logic analyzer to try to spot the problem. That's the next step for me as well; try to determine what is making my bus "noisy." But that being said, the noisy bus on my '94 never resulted in failed erases or replies; it only ever resulted in silly things like being unable to reboot the kernel automatically after the process was completed. Yours looks far more serious.

But while we're on the topic, what are you using to connect your computer to the ALDL connector, precisely?