I think there is something in the tune that HP Tuners does not give us access to. I had a 2011 Camaro LS3 A6 tune that the speedo works perfectly, the vehicle speed output is set to serial and it works perfectly. I have a 2010 LS3 A6 tune that I matched every setting to the 2011 and the speedo still puts out a constant voltage. So I gave up and put the 2011 tune in the car. VOILA! Speedo works perfectly. I matched up all the applicable settings and the trans shifts and all is good. I have copies of both files.. I no idea why the 2010 would not work.