Possible reasons:
1. Transmission fluid problems:
*Low fluid level
* Contaminated or old fluid
2. Mechanical problems:
* Worn friction discs
* Faulty solenoids or valves
* Torque converter problems
3. Electrical problems:
*Faulty throttle position sensor
* Faulty input shaft speed sensor
*Wiring problems
4. Software problems:
* Malfunction in the automatic transmission control unit software
Diagnosis and elimination:
1. Check the level and condition of the transmission fluid. If the level is low, add fluid. If it is dark or smells burnt, replace it.
2. Connect the error code scanner. This may reveal any stored error codes that indicate specific problems.
3. Check the condition of the automatic transmission solenoids and valves. Worn or faulty solenoids can cause shifting problems.
4. Check the torque converter. If it is faulty, it can also cause shock when shifting gears.
5. Check the throttle position and input shaft speed sensors. Faulty sensors can send incorrect data to the control unit, which leads to problems with gear shifting.
6. Update the automatic transmission control unit software. In some cases, official software updates may resolve shifting issues.
Important: It is recommended that you contact a qualified mechanic to accurately diagnose and correct the problem.