Possible causes and solutions to the problem of automatic transmission stiffening during acceleration:
Malfunctions of the mechanical part of the automatic transmission:
* Worn or damaged clutches and steel discs
* Clogged oil filter
*Low transmission fluid (ATF) level
*ATF leaks
* Damaged torque converter
Solutions:
* Replacement of worn components
* Replacement of oil filter
* Topping up or replacing ATF
* Elimination of leaks
* Replacing the torque converter
Electronics faults:
* Damaged solenoids
*Faulty speed or throttle position sensor
*Wiring or ECU problems
Solutions:
* Diagnosis and replacement of faulty solenoids
* Replacement of damaged sensors
* Checking and repairing electrical wiring and ECU
Transmission slipping problems:
* Worn or dirty clutches
* Insufficient ATF pressure
*Low ATF level
Solutions:
* Replacement of worn/dirty clutches
* Diagnose and fix ATF pressure problems
* Topping up or replacing ATF
Other possible problems:
* Clogged catalytic converter
* Faulty mass air flow (MAF) sensor
* Problems with the ignition system
Solutions:
* Replacing a clogged catalytic converter
* Replacement of faulty MAF
* Diagnostics and repair of the ignition system
General recommendations:
* Maintain the automatic transmission regularly, including replacing the ATF and filter.
* Avoid sudden acceleration and towing heavy loads.
* If there are signs of automatic transmission malfunction, contact a qualified mechanic for diagnosis and repair.