Speedo Issues

[DKz Garage]

Wondering if anyone has some input..... I have a 69 Camaro with Dakota Digital VHX gauges. PSI harness and a T56 magnum, using a ECU out of a 2002 Truck that has been flashed and tuned. I have the one wire lead from the ECU hooked up to the Dakota Digital box as instructed for the speed input. After trying several times to calibrate the speedo using a "measured" mile, I still can't get it correct, even tried using my GPS to manually calibrate the speedo. Evidently, the trans speed sensor is not sending enough pulses to get a correct reading. Talked to the guys at AMP performance where I purchased the trans and was told that the T56 Magnum has a "Ford" style 12 tooth reluctor, not a 18 tooth GM style?? I know a lot of guys use the T56 and Dakota Digital stuff...... Any thoughts??

Thanks, Dave