I had previously replaced the hot water stem without a problem. I'm not sure what to do next.

Hi Bdmeyers

Pull the stem out and run some cold water out of the valve with the stem out (put towel over valve)... see if it clears any debris/sediment that could be getting caught under the stem washer.

If that is not the issue then the next step would be to replace the SEAT that the washer of the stem sits against... ;)

Back to you...

Mark