Truck slams into reverse.

Dm23

Active member
Mar 8, 2019
334
76
28
Socal
My truck off and on will only slam/jolt in Reverse. Temp is at 155 or so. No codes no lights. Sometimes it does it sometimes it doesn’t. Anyone have any thoughts. Transmission built by mike. November 2021 With the R converter. Is this not a big deal or something that needs attention?
 

Dm23

Active member
Mar 8, 2019
334
76
28
Socal
I am not 4 wheel drive so no transfer case, but I will look at the fluid level.