Hello I recently replaced my ecm with a unit out of a higher hp engine to increase power. Has made a noticeable improvement but my speedometer is reading about 6 mph lower than actual speed. I think this is causing my automatic transmission to have some shift issues. Is there a way to recalibrate the speedometer myself. About 2.5 hrs to go to dealership.
2004 4300 with dt466e and Allison 2400. Thanks