After replacing the pump assembly in a 6L80/90 transmission with a new GM pump the vehicle returns with symptoms that would appear to be caused by a low fluid condition: it falls out of gear at a stop and has low line pressure. Upon further inspection the sump filter, which was also a new replacement, is found lying in the bottom of the pan.
Some new GM pump assemblies have been mis-machined as seen in Figure 1. The machining process that creates a step and smaller diameter bore for the filter pickup tube was not performed. This causes a loose fit of the filter neck in the bore even with the booted seal on it.
When purchasing a new 6L80/90 pump assembly, be certain to check the filter pickup tube bore for the step that creates the smaller diameter part of the bore as seen in Figure 2.