I replaced two american standard stems(with a "top cap" seal). The cold is fine, but the hot has little flow with the new stem and seat.The old stem was wearing into the seat, and the top half of the seal on the stem was separated.
I had to put the old stem and seat has well as the broken seal to get any water flow. Also I did make sure when tightening thepacking nut that the stem did not turn,(if it turns it won't install correctly,)
And the flow is fine without the stem in.

Picture of new stem.