How many miles on the motor? how much timing are you running? there is a huge diff between 2.73 and 3.73. Something else is suspicious then. As far as your speed and rpm I dont remember the 65mph relationship on the tach but going 80 it was just below 3k IIRC.
I am running about 13 degrees of timing and i am not sure how many miles are on the motor. There is about 134000 on the car but the guy i got it from said he used to run nos on the car with hci on it but did not get any of it when i bought it. And the compression is ok not great but where it should be and even across the cylinders.