The hot water is running cold in the one bathroom sink with decreased pressure?

Sounds like you have a blocked cartridge. Shut the water off under the cabinet ands open up the faucet. Remove the cartridge and check and clean the inlet ports. While the valve's open place a pan over it and turn the hot water on to flush out the supply. You should have a full sream when you do this. If not let me know. Good luck, Tom