It may need to have the ecm from a manual shift truck. All i can figure is that the ecm is reading shift fault codes and therefore going wacky with the tach signal. Have you plugged in a decent scanner to see why rpm the ecm sees compared to the gauge on the dash?
Thanks for the idea redneckcustoms. I only have a basic obdii scanner and it doesn’t give me the rpms. I will see if I can ask my friend with a scanner that can do that. I must add that although the tach rpm is off, it is consistently incorrect and doesn’t jump around. There are expected shift solenoid CELs as you said. I would like to splice a manual exam in, but I don’t want to open a can of worms just for a correct tachometer reading because the motor runs fine. I am still trying to figure out if the ECT button does more than change shift points because I swear it seems like there’s more power with the button on, but that could be in my head.
