Hello!
I just registerd at this forum today. Just reading your problem with rough idle, hesitation and knock.
I have a 1994 Buick Custom that had pretty much the same symptoms.
I changed and checked everything to do with the fuel and ignition systems. These cars have electronic EGR Valves. I found after taking it apart that there are three spring loaded valves that have to float. Mine were stuck due to heat. I managed to free the stuck valves and it ran better than a new one.
It may be a shot in the dark but you have tried everything else.
Thanks