Are you sure it is detonation? That range is right where you are probably dumping a ton of fuel and it could just be that your car is bogging down because of it. You may even get some popping or something out of the exhaust from raw fuel. Does it come to life and seem fine about 5500ish?

 

i have the same prob but at 5500 is when it bogs out...any ideas? im hoping its just gap on the plugs and maybe too rich? sorry to jack the thread but its killing me...thanks