I've been watching this thread since I have the same issue. My 94gt has detonation as well under WOT starting at about 3500rpm. I found that the timing was advanced to 14 degrees so I turned it back to 10. I still get the detonation but it is not as bad. I've wondered about the plugs as well. I have also noticed some damage to some of the plug wires from the previous owner. It looks like some insulation was shaved-off for whatever reason I do not know. The engine seems to always run on the cool side. I'm wondering if the previous owner put in a 180 degree thermostat.
Is it possible the bad wires and/or colder thermostat cause the detonation??? I'm going to do a full tune-up this winter while I have it stored and I don't want to start the new fun season with this annoying detonation.
Also, I'm a bit of a rookie, can someone explain this colder spark plug thing to me as well
Thanks much