I've got a an 0.68 for 5th gear and a 3:73 ratio rear end. With 15 inch tires and a very accurate speedometer and tach, and I'm doing 100 MPH (not 65) at 3000 RPM.
As many have said before me .... "something is wrong".
Here is a good calculator ...
http://www.cobranet.com/rpmmph.html