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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!!
 

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At what speeds? I've noticed my PM has a huge amount drag so if I'm going over ~70mph, it usually has to drop into a lower gear repeatedly to maintain speed with even the slightest uphill or headwind.

UPDATE: Woops, I realized you answered this. The only thing I can think of is that one of your brakes might have locked in place? Do you use your hand brake a lot for parking? Might got stuck last year so I had to stop using it.

If you're on a very slight incline, does the vehicle roll when in neutral?
 

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Does not matter what speed. Hand brake only used when launching kayak from trailer. Would be ok, except downshifts from 6th to 3rd or 4th at highway speeds!
Rolls in neutral with no problem.
 

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I am not sure yours is normal but the few times I have ridden in one of the gassers I was dumbfounded at the number of shifts. This is an area where the diesel was so much better as it has the torque to pull a considerable grade and the downhill is easily managed by the manual shift. Most PM drives seem to ignore or consider normal the 4000-5000 rpm up and downshifts. It is the future for all vehicles it seems.
 

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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!!
Mine is brand new and was doing this going down hills without tow/haul. Shifts from 6th to 4th - 4500 rpm. You're right about the ice.
Someone said to use the accelerator to tell the van you can to faster - It didn't upshift - RPM's went up.
Having owned 2 Caravans, this never happened
Jon
 

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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!!
We have a 2018 3500 153 ambulance that did this the other day while going down hill. I wasn't driving and just thought the driver had the cruse control on but he didn't. I didn't notice if the tow button had been engaged or not. A the bottom of the hill the van accelerated again like normal. I'll have to keep an eye on this.
 

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After reading your letter I would say my 17 159" Hitop does exactly the same things. While it stunned me the first few times it is normal in this van and happens just as you have written.
65-70mph rolling down the freeway and it downshifts. Roll downhill and stop accelerating and it will downshift and maintain your speed.
Doesn't hardly phae me anymore unless I'm on cruise control.
 

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2017 promaster 2500 159 with 99,000 doing the same thing. Makes no sense why it downshifts just letting of the accelerator. No cruise or tow haul button on.
 

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N-O-R-M-A-L
As in life, normal is not necessarily a good thing.
 

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The auto downshift on downhills is really the one thing about my Promaster that I don't like. I compensate by keeping a little gas on the accelerator, which seems to keep it at bay, or premptively downshifting. Would love to know how to disable this.
 
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