My kitchen faucet is running very slow with both the hot and cold water. I checked the filter and it is clear of debris and I checked that the water was turn completely on. What could be the cause of the slow running water?

By filter did you mean aerator, if not remove the aerartor to see if the volume improves. You might have debris in the mixing valve both it usually affects hot before cold and almost never in the same volume reduction. Come back after the aerator is removed and tell us more.

The aerator has been removed and the pressure seems to gradually getting slower

Sounds like you've picked up some trash . Try this. Shut the water off to the faucet and open it up. Remove the cartridge and check and clean the cartridge inlet ports. Now turn the water back on for a minute to flush out the supplies. There should be a strong stream when you do this. If not then tell me about it. Reassemble and test. Better now? Good luck, Tom

How I fixed my problem!
I turned off the electric to the heater for safety precaution as you should if a gas hot water heater turn off the gas. Drain the tank then take all lines loose from the top of the tank. (Inlet cold side and outlet Hot side), look inside the pipes coming from the tank and you will see a plastic check valves, They tend to get rust in them or freeze up. Remove them entirely one on each side. Note: they are a pain in the butt to remove but they will come out. After they are removed reconnect lines and fill. Note: After removing them it took my tank 3 minutes to fill when before it took 2 hours. Pressure is restored simple fix and doesn't cost you $600.00 for a plumber to do it for you, because he won't even tell you that is the problem. All he will you is check please! Good luck to all the vets , disabled and people on a fixed income. That doesn't work email me bennyhill38 at Yahoo dot com

Robert