Hyundai Repair: Automatic Transmission dropping into 3rd gear, hyundai sonata, continuous problem

Question
Hi
My 1999 Hyundai Sonata will drop itself into 3rd gear when I.m driving anywhere from 70-120 km an hour.If I put it in neutral and shut off the engine and then restart it it will shift back into drive. Sometimes it won't and I have to pull over and stop and turn the engine off and restart it before it will stay in drive. This is a continuous problem thats been going on for a while. Any quick fixes or am I looking at a new transmission..................

Answer
It's probably something simple.  You should check for engine and transmission diagnostic trouble codes.  These will give you information as to the nature of the problem.  If the transmission computer detects a problem, it'll put the car in third gear only.  The transmission will remain there until the vehicle is turned off and restarted.