2009 Kia Rondo OBD2 Fault Code P0731: Gear Ratio Issue and Limp Mode Diagnosis

Hi there, I recently purchased a 2009 Kia Rondo that has started entering limp mode unexpectedly. After connecting an OBD2 scanner, I'm seeing fault code P0731 — indicating an incorrect gear ratio in first gear. The car shifts smoothly when manually driven and performs well on stands with the transmission in drive, shifting perfectly through all gears up to 5th. However, as soon as I place it into drive and start moving, it immediately jumps into limp mode. I've already replaced the transmission fluid, checked both input and output speed sensors, and verified wiring connections to the ECU — all of which appear normal. The issue seems specific to real-world driving conditions. Given that the car behaves correctly when stationary but fails during operation, I'm wondering if it could be a faulty solenoid valve. However, if that were the case, wouldn't the problem occur consistently regardless of driving conditions? Has anyone else experienced this behavior with their 2009 Kia Rondo and P0731 code? Any insights or troubleshooting steps would be greatly appreciated. Thanks in advance for your help!