Transmission shift problems and noi

There is a vacuum modulator on the front of the transmission if you look straight down when the hood is open, although not common to fail it is a possibility. Check to see if there is ported vacuum at the valve or check to see if the vacuum line came disconnected. Also if the vacuum line is really soft and bloated looking this usually means the modulator valves diaphram is leaking and this too could cause your problem.

The most common cause of sudden harsh shifting while driving or after it is warm is normally a sensor issue. There is a chance that there is a fluid issue but if operation returns to normal due to a key cycle or after it sits then this points to a sensor is not reading properly that would effect transmission operation. Clearly there are numerous sensors that could effect it but the most common one is the throttle position sensor.

The reason for this is the engine and transmission control module rely on knowing what the throttle input is from the driver so it can match the air/fuel ratio and know if it needs to downshift or upshift to meet the demand.

I attached the info needed to diagnose this issue. You can also monitor TPS voltage as you depress the throttle. The voltage change should be smooth and no jump erratically. If it is then the control module is getting erratic voltage as well.

Let us know if there are questions. Thanks