High speed rear end and speedometer

JasonNC

Ok, I put a 3:07 53 Hornet rear end that was formerly attached to an automatic transmission in my 49 Super Six.  I use my GPS to check my speed as the speedometer never gets above 45 mph (while the GPS tells me that I'm doing 70 mph).  The overdrive transmission that was in the car was replaced with a standard transmission and I'm reaching that speed at a little less than 2K rpm on the tachometer.  Any suggestions on how to find a transmission gear that will at least lower the difference between the speedometer reading and my actual speed?

RichardD

https://www.pistonheads.com/gassing/topic.asp?t=1578144

Jason, you are likely aware of these correction boxes. The link site is a good explanation about these if you need to go this direction.