I have a 2018 Promaster 159” High-top and it has a tendency to DOWNSHIFT all by its self. I can be driving down the road at 55-60 MPH and all of a sudden it will downshift to 3rd or 4th gear and RPM goes up to 4000-5000 RPM. Have told dealership and they can NOT find the problem. Told me they have documented it and at least I have drive train warranty...if needs fixed. Van currently has 17,500 miles on it. Problem has been going on prior to even having my first oil change. WHAT TO DO NEXT!? If this happens on icy road, I am sure loss of control would occur and possible CRASH!!