This sounds like a torque converter issue. If you or a shop has a scan tool that can monitor input shaft speed (Engine RPMs) and output speed you can calculate the torque converter slip when this is happening.
However, most scan tools will do this for you and show you TCC slip. When the transmission is locked up in overdrive there should be minimal slip and I suspect you will have quite a bi.
If not, below you will find the testing that we can run through as well for the torque converter.
Let us know what you find with this and we can go from there. Thanks
Images (Click to enlarge)
Thursday, May 6th, 2021 AT 7:18 PM