You absolutely have a slippage problem.

RPM= (MPH x gear ratio/ tire diameter) x 336

1.64 seconds isn't that bad for a 11 second car. I found out years ago that tires can make a BIG difference. I ran a front engined dragster and called Good Year about the best tire for the car. I went from 9.83 E.T to 9.30 by changing to the right slick.