In my stand-up shower the cold water just trickles. There are 2 handles, a hot & a cold. There is minimal pressure or volume when I open the faucet completely. I replaced the stem, put everything back together, & am still experiencing the trickle effect. What is causing this to continue? I thought once the stem was replaced everything would be back to normal.

If this occurs both hot and cold it is likely that there is some kind of blockage in the shower head. Remove shower head and see what kind of volume you have. If this is a tub and shower, the blockage could be in the diverter valve.