Another E38 aftermarket speedometer question

[ScottTX]

I have searched and searched for the answer to this problem on my own but now I need your help.

I have a Speedhut speedometer that I am trying to get to work correctly with my transplanted 5.3/6L80e combo using the E38 ECM speed output. I have tried all the combinations of options in the Speed tab of HP Tuners but only one (Speed Output Type: VehSerial; Vehicle Speed Output: Serial) will read the signal out of the ECM. However, the speedo reacts really strangely. First, on acceleration the speedo lags the actual speed badly. Then, on deceleration the reaction to the actual speed lags even more. Lastly, when coming to a stop the needle will stall at about 20pmh and then drop abruptly to zero after I have already been stopped for several seconds. Does anyone have any clue what could cause this?

Things I have tried:
All combinations of Speed Output Type and Vehicle Speed Output
Pull-up resistor on speedo wire from ECM (had no effect)
Metered the ECM wire and get a 12v signal on idle and about 6 volts when moving which seems correct since this a wave from 0-12V
Contact Speedhut Tech Support (they want me to wire directly to VSS which is not possible (i think) on 6L80e)

Any help is appreciated.

[ScottTX]

No one, nothing? I am going to have to rip my dash apart to send this back to Speedhut which I would very much not like to do. If you have any thoughts, please share.