Reverse Issue

[H3LZSN1P3R]

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This is the same as my situation. I was moving the truck from one spot to another in the driveway.

Do you recall if your door was open or ajar?

If it was quickly shifting after starting its due to the truck building line pressure. Its usually worse if the truck sits for a bit as the tq converter drains back some. There is nothing wrong just wait a couple seconds for it to engage reverse before releasing the brakes.

 

[Firebird]

My 2021 Cummins backs up just fine with the door open, but my 2019 with 6.4 and 8 speed would not