My 2014 Dodge Journey has engine light come on only on highway driving. When the engine light comes on, the tranny doesn't want to downshift.
Driving around town a few hours and engine light goes off. The only underhood service recently was engine oil cooler/filter housing replaced.

 

You need to get the codes read from the check engine light. If you do not have a code reader, most auto parts stores will read for you. It could be anything.