Throttle potentiometer (pedal) and throttle body faults usually produce an error code and the infamous MCSF warning on the dash. The only exception I can think of would be a mechanical fault with the throttle body mechanism, preventing the butterfly from opening properly but I think this is unlikely. If the throttle opens enough to accelerate to 4500 under load, it'll open far enough to easily exceed that with the car stationary.
The butterfly will not fully open without the engine running, even with your foot to the floor. This is normal.
Ideally it would be good to get the car connected to an oscilloscope and observe the signal produced by the crank sensor, to see if it is breaking down or producing a false signal when the revs reach 4500.
Did you check all the earths properly as I suggested?