Engine Speed (Revs) Increase when Coasting Down Hill at Highway Speeds (70MPH)

[Rosselk]

I am posting to the group on behalf of my son who owns a 2017 1500 4x4 with 170K miles. His issue is a little difficult to describe in words but I'll try.
When driving at highway speeds (interstate) and holding the throttle steady, he will occasionally notice that the engine speed (revs) slightly increase from 1800 to just under 3000 rpm when the truck is going down hill but he is not gaining speed. When he presses on the gas pedal slightly, the revs increase (and so does vehicle speed) but it feels like the transmission has shifted into the next lower gear (7th) and won't upshift to 8th. So imagine your cruising along at 70MPH with steady throttle applied and the road grade declines to a downward slope and without applying any more throttle, the engine speed increases. Yes his check engine light is on but the only code(s) retained per the dude at AutoZone was a loose gas cap.
So after replacing the gas cap I went for a ride with him and my observation was that the transmission upshifts and downshifts normally (quite smartly actually for 170K miles) with no latency between gears and at predictable speeds/conditions.
Has anyone else experienced such a drivability issue?
Thanks, Mike

 

[stevj]

Sounds normal to me.
Got lots of hills in my area so here are some things I've noticed with my Ram.
Taking the foot off gas pedal when going down hill: Firstly, the vehicle already knows you're headed down hill by the attitude sensor. Second, foot off the gas tells vehicle you want to slow down, so it will downshift to assist in that endeavor.
Put your foot back on the pedal and give it a bit of gas. Remember, the vehicle still senses down hill attitude so remains (usually, but not always) in a lower gear until level again.
Also, accelerating up hill will cause the transmission to stay in a lower gear longer (in my Ram until about 2400 RPM) before shifting to the next higher gear. Again, it's the attitude sensor at work.

Steve