usually it is the overdrive solenoid, but can be the connector to it, input to the computer, or the computer.
electronic solenoid
a bad radiator -automatic portion of radiator not cooling off transmission
The most common cause of a automatic transmission jerking, when shifting, is low transmission fluid. Fill the transmission to the full mark.
your transmission is about done, sell it
A gear which causes the transmission output shaft to rotate at a higher speed than the transmission input shaft.
Assuming it is an automatic transmission, I would check the fluid level. When the transmission is warmed up, the level should read 'full' on the transmission dipstick. Check the color and smell of the oil. Does it smell burnt, or does it appear to be brown instead of red? Perhaps the filter screen is clogged.
There is a push button on the end of your automatic shift lever. Pushing it in causes the Overdrive to turn on and off.
Possibly low fluid.
Your transmission is breaking down inside. ether watch for it. or extensive transmission is required.
There are several causes that an automatic transmission will not want to shift into second gear. The two most common causes are transmission pump issues and trouble with the vacuum modulator.
The transmission needs repair. The electronic control system causes the transmission to stay in 2nd gear when it detects a problem, such as slipping in 3rd gear or overdrive. This allows the car to be driven in an emergency.