Do you know what transmission sensor you replaced? There are 2 speed sensors on it.
Have you had any other work done?
Another possibility is the pinion factor in the trans controller somehow has gotten reset and needs to be programmed.
how I reset and reprogram the output speed sensor
So this is what you've changed?
Since the sensor was changed already there can only be an issue with the wiring or the speedometer head itself. If you have a DVOM all you can do is check toe wiring from the sensor to where it connects to the instrument cluster.
Try doing this test:
Perform the Instrument Cluster Self Test.
Turn the ignition off.
Press and hold the Trip Reset button.
Turn the ignition on.
Observe the gauge in question while the Instrument Cluster performs the Self Test.
The gauges should position at the following calibration points:
Speedometer: 30mph (51km/h BUX), 60mph (102km/h BUX), 90mph (153km/h
Tachometer: 2000, 4000, 6000, 8000
Fuel: E, 1/2, Full
Temperature: Lo, Mid Lo, High
Did the gauge in question operate properly?