I'd try a wrecking yard one first. Last time I bought one was $20 for just the speedo gauge uninstalled from the cluster. I don't know how to test them.
Your mileage will change, and the coding for your wheel size will also change. You can recode the wheel size, but mileage will be whatever the new gauge has on it.
Unless you're feeling adventurous and desolder the EEPROM chip from one to the other.... I've done that once, wasn't too hard.
His issue is with the tachometer, not the speedometer so he can disregard those speedometer related instructions,
...and to the original poster:
If the E4OD sensors are determining the RPM directly from the tachometer by sensing changes resistance (or voltage) through the magnetic coil in the tachometer itself then a replacement tach could fix the problem BUT I'm much more inclined to think that the transmission is getting the RPM signal directly from the tach sensor through the wiring to the electronic control module behind the driver side kick panel and from there through wire(s) that go from the control module to whatever location controls the shifting.
I would also FIRST suspect a problem in the wires that conduct the signal from the tach sensor to electronic control module and from whatever component the E4OD uses to pick up the RPM signal back to the control module. I used to know this whole circuitry and all of the components but since I don't have an E4OD I've honestly forgotten most of it.
I HOPE your problem is in the wires and it will be easy to find, like a posi5tive wire that's grounding out somewhere or short circuited to another wire due to some damaged wire insulation.
I have a headache right now so I can't proofread this before posting it.
