FCA has issued an addendum to the 2019 JL owners manual — specifically regarding fuel requirements for the 2.0L engine. The issued addendum card clarifies the use of 91 octane for “optimal performance” as follows. “This increase in performance is most noticeable in hot weather or other heavier load conditions, such as while towing”.
The takeaway from this clarification statement is that there are less gains/benefits from using using premium gasoline in colder weather on the 2.0L JL Wrangler.