So my suburban has an aftermarket trans temp gauge for the 700r4. Replaced the transmission back in October and haven't been able to get the temp gauge working ever since. It has power, when I turn the truck on, the gauge does a full sweep from 0-max temp, drops back to 0, then back to max temp and stays at max temp. Have tried requiring the sending unit but to no avail. Any ideas? Does the transmission have to be grounded as well as the sending unit?