Possible reasons for tight automatic transmission shifting on Toyota Corolla:
Transmission problems:
* Wear or damage to transmission components (e.g. gear clutches, friction discs)
* Dirty or low transmission fluid level
* Faulty torque converter
* Clogged or faulty transmission filter
Problems with the hydraulic system:
* Low pressure in the hydraulic system
* Leaks in lines or system components
* Faulty hydraulic valve
* Worn or dirty control solenoids
Electrical problems:
* Faulty electrical connectors or wiring
*Faulty Transmission Control Module (TCM)
* Problems with shift position or speed sensors
Mechanical problems:
* Worn or seized cable shift mechanism
* Faulty gear shift assembly (external mechanism connected to the gear selector lever)
Other possible reasons:
* The engine does not gain the required speed (problems with ignition, fuel supply)
* Wheel slip (can lead to increased load on the gearbox)
Diagnostics and repair:
* Check the level and condition of the transmission fluid. Replace fluid and filter if necessary.
* Scan the vehicle for transmission related trouble codes.
* Check hydraulic system pressure and control solenoid pressure.
* Check the operation of the transmission and hydraulic system components.
* If necessary, replace faulty components or repair the transmission.