I have low hot water pressure in my kitchen sink. The cold comes out strong, but the hot only trickles. It's a two year old Kohler faucet with only one handle and has a sprayer. I checked the pressure coming from the wall under the sink and it feels very strong.

Check the supply tubing coming off the hot water stop under the sink . It might be kinked,
If it a braded speddy simply straighten it . If its riged copper it may need to be changed.
Itif that's not the case then try turning off the water and removing the cartridge from the faucet it should rattle when you shake it if not tap it on the palm of your hand and re insert it .

Unless something was done under the sink the line is not likely to kink by itself. Its most likely that debris from the water heater is blocking the hot inlet on the mixing valve. Remove the valve or cartridge and clear it. If not sure how to do this try downloading a manual from Kohler. KOHLER: Product List: Kitchen Sink Faucets: Faucets: Kitchen

On the second floor apt. kitchen and the first floor apt. kitchen and bathroom, the hot water runs full for a second and then stops. The cold water is full force.