I have a 2014 hyundai elantra with 220k mostly highway miles om it. I drive very conservatively and i am a bit of a stickler about oil and fluid changes etc.

Engine runs good but suddenly one day on way home from work the engine would revv but would mot imediately shift upward. Finally it shifted upward but would not shift past about 3rd gear i think. I was able to reach 40mph at just over 2k rpm. I got home safe using side streets.

Upon further experimentation i noticed "manual mode" still worked fine with the gears shifting normally when i moved the stick at 2k rpm. I was able to reach highway speed no problem

Is this a possible TCM or solenoid? All the gears work fine in manual mode. Engine still runs good.

Please help. I want to avoid a potential $3k repair if possible. 

Thanks