Going 70 MPH down the interstate my RPMS run at 2500. Does that sound right? Can you figure my gearing? Thanks

 

My graph would have you closer to 2600-2700 RPM for 3.54 gears and 235/85/16 tires. Your tach might be underestimating a little, I know mine does. It doesn't like to read much higher than 2600 either.

Maybe Dave can fire up the spread sheets to see for sure.

 

2500 with a C 6 and 3.55 gears would be 65 MPH with 235 tires.

Have you checked the speedometer?

60 seconds at 60 MPH to drive one mile on the interstate or find one of those radar signs that show your speed.

 

Im thinking my speedo is off a little, I will find one of those radar signs.