2019 RST Up/Down jerky wierdness at 35-40mph. DFM? Torque Converter?

[Stanleyj42]

Around 15K I had the transmission issue with it slipping  and the dealership replaced the fluid with the mobile 1 which seem to resolve it enough that i could live with.  The transmissions still clunks into first when down shifting but whatever.  Well now at 30K I have something similar going on, but seems just slightly different.  When I'm cruising around 35-40 it almost feels like the truck is braking or downshifting and then speeding up, but enough everyone in the truck can feel it. At first i was thinking it was the DFM kicking in and its opening and closing valves so i bought a pulsar box ( i needed it for tires and autostop/start as well) and disabled the dfm, but it still does this weird shimmy.   I know that doesnt necessarily still mean its not dfm but... still.

 

This may sound crazy, but its much worse when its really hot outside and the truck has been sitting for bit. This morning it was cloudy and about 80 degrees.  Didn't notice it too bad when i left, but this afternoon it was about 95 (truck had been sitting in the sun for several hours) and when i went to leave even the passenger was thinking i was about to run out of gas once we leveled out around 40.  After stopping and going a few times it settles down enough that its back to just being very subtle, but still noticeable.

 

Is anyone else experiencing something similar?  Is it DFM, Torque converter, transmission or just something i will have to trade out to resolve. 

 

 I appreciate any answers that are offered up because i really, really don't want to get rid of this truck. 

 

Edited June 8, 2021 by Stanleyj42
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