I have another question...
I have oversized tires on my Suburban. I bought and installed a TruSpeed when I installed the tires (probably 5-6 years ago) and got my speedo dialed in dead on as tested against GPS regularly. My odometer is also dead on as compared to the measured mile signs on the highway.
Now my OBDWiz software is reporting the speed off by a considerable amount (says 65 when I am going 70). The TruSpeed plugs into the ECU. Does the OBDWiz read the VSS before the TruSpeed has a chance to adjust it? Is there a way to get accurate speed in OBDWiz?