Transmission/Detroit ECM Settings

Had a guy that come into our shop that has a Detroit with DDEC 3 ECM on his truck. He wanted his speed set up to 75 MPH. I hooked up the computer and found his truck had had the ECM changed. He has a direct transmission in it with 3.08 ratio rears. The computer was set up for overdrive ratios, wrong size tires etc..

I set the tire rev/mile to 498 (11R22.5)
The top gear ratio to 1
and his axle ratio to 3.08
I am not sure about the VSS Teeth It is set at 16. (does anyone know what this should be?) It is a RT14710B Eaton Transmission

Anyway after making these changes he says he can't go faster than 72. I have the speed limit turned off. But if I did check it on it says max speed is 70. The VSS type is set to Tail and the signal is magnetic.

 

You are correct. I thought about that after I posted this. I broke out the old road speed calculator just now and with what he has at 1600 RPM 70 MPH is top speed. At 2000 RPM he could get 78. He is going to have to drive 70 or make some changes. Thanks