Possible reasons for delayed gear shifting in an automatic transmission:
Mechanical problems:
* Worn clutches or steel discs
* Faulty valve body
* Contaminated or old gear oil
* Faulty shift solenoid
Hydraulic problems:
* Insufficient oil pressure
* Clogged oil filter
* Faulty oil pump
* Leaks in the transmission system
Electronic problems:
* Faulty vehicle speed sensor
* Faulty gear selector position sensor
*Faulty Transmission Control Module (TCM)
Software problems:
* Bugs in TCM software
* Incorrectly selected gear shift program
Other possible reasons:
* High load on the vehicle (for example, when towing)
* Transmission oil freezing at low temperatures
* Worn or damaged timing chain (for some models with timing chain drive)
Additional symptoms that may accompany delayed shifting:
* Increased fuel consumption
* Vibration or shock when shifting gears
* Slipping during gear changes
* Engine speed fluctuations
* Transmission of the gearbox into emergency operation mode