Inspection of a 904 torqueflite

glhx said
With the feeler gauge, the end play with the snap ring installed is .044
This was done with the snap ring on and the gear train turned over to get a good measurement at the back of the gear train

It seemed like it was a lot tighter than that before and fit snug.
There shouldn’t be a reason it’s .03 under the maximum spec.
But we’re looking right at it and it’s not put together wrong.

That slot the snap ring sits in is is between .086 and .090.
Wit has an .084 snap ring but it’s not available and I suspect it won’t be but I could source it somewhere else.
It would close the gap up no problem.

Question is.....am I masking something else?
It feels fine and meshes fine but it’s also not spinning thousands of rpm.

If you look very carefully at the snap ring when it's sitting in the groove you will notice that the snap ring only contacts the groove on one side. The other side is actually against the gear set. That is why I asked you to measure the end play with the snap ring installed.
The other side of the groove will never touch the snap ring because the gear set is slightly longer than the location of the groove so that the thickness of the snap ring controls the end play. Unless your thrust washers get excessively worn.