No matter what I do I cannot get my ecm to match my speedometer. When I bought the truck the speedometer read 3 mph slow at 60 mph. This was with bone stock 265/70r17 tires 31.6" tall. In order to correct the speedo I had to enter 32.31" tire; VSS Tire Revs per > Dist = 388, Dist - Trans = 624.22. Speedo read correct but now I am off 6 mph according to hptuners scanner mph which is about 10%. The problem is this screws up all my shifts, they all occur 10% early. I just installed 33" tires and in order to correct the speedo I had to enter 34.65" tall tire. I've tried messing with the Dist - Trans numbers and it does not change a thing.
What do I need to change to align my ecm speedo shift mphs while having my speedo read accurate? Is this possible, what the hell is going on?