I30 A/T gear shifting problem

[bassa1]

2000 I30 70K miles When accelerating and driving normally the problem doesn't occur, but if I floor the gas pedal or accelerate hard, the car will go into a low gear (maybe 1st) and stay there, only when I eased up on the accelerator, the car will go to a higher gear. The gear changes are seems very smooth. The car had a P0731 code (incorrect 1st gear ratio). Changed the transmission oil, but didn't help.

[Q45tech]

Are you saying that the transmission will not shift with throttle 100% open [floored] until the rev limiter cuts off fuel to engine?

Shift position sensor/underdrive clutch inside AT?

"DTC P0731 A/T 1ST GEAR FUNCTIONDescription

* This is an OBD-II self-diagnostic item and not available in TCMself-diagnosis.* This malfunction will not be detected while the O/D OFF indicatorlamp is indicating another self-diagnosis malfunction.* This malfunction is detected when the A/T does not shift intofirst gear position as instructed by the TCM. This is not causedby electrical malfunction (circuits open or shorted) but bymechanical malfunction such as control valve sticking,improper solenoid valve operation, etc."

First stepm is to get a transmission full flush to see if something is sticking inside!