I am trying to figure out why I have reduced pressure from my kitchen sink faucet. Initially, when I turn on the faucet, either hot or cold, the pressure is good for about two seconds, after that it reduces by approximately half. I have replaced the seat and springs but that only eliminated a drip. Now I don't even have the initial two seconds of good pressure. The additional hose which is hooked to the same supply has great pressure. Please help.

Thanks,
John

Sounds like debris in or just before Faucet. After all dissassembly, cleaning and reassembly,
Disconnect lines and blow through faucet with faucet set to full cold, full hot and warm.
You probably already unscrewed end of faucet and checked screen.