2000 Hyundai Sonata 2.4 L engine, transmission drops from 4th gear to 3rd gear at cruising speed (65mph) and locks into 3rd gear, I have to stop and turn the key off and start the engine again to reset the A/T what do you think is happening?
Have you checked the transmission fluid level? Is it red or pink without a burnt smell? That’s the first place to start.
Has the transmission been maintained according to the owner’s manual?