If a car upshifts early and won’t go into passing gear at wide open throttle above 45 MPH, what might be causing this issue?

In an automatic transmission, various components cooperate to ensure smooth and timely shifts. If a car is experiencing early upshifting and will not engage passing gear at wide open throttle above 45 MPH, it indicates a problem that’s likely mechanical or related to the control systems within the transmission.

When shift valves are stuck in the valve body, it impedes the proper movement of hydraulic fluid that controls gear shifting. These valves are crucial as they regulate the flow of transmission fluid based on inputs such as throttle position and vehicle speed. If they are unable to move freely or are stuck in a position, the transmission may not receive the correct signals to execute shifts appropriately, leading to issues like early upshifting and failure to engage higher gears when needed.

This specific situation aligns closely with the symptoms described: an inability to move into passing gear may result from the transmission not properly recognizing the need to shift or downshift due to the stuck shift valves. Therefore, addressing the issue of the shift valves would likely resolve the problem of improper shifting behavior experienced while the vehicle is in motion.