98 mustang rev limiter?
An extra 2000 RPM will not do you any good. Stock engines are pretty much at maximum output by 5000 RPM.
Even if you had another 2000 RPM that was actually power, you could not go above probably 110 MPH as the speed is also limited.
Usually the only time RPM is limited is when in neutral and reverse.
The Tach is "redlined " above 5000 because that is also the danger zone for stock engine integrity.