When I use the spray hose attachment on the kitchen sink, the water still runs at normal pressure from the main faucet.

Thank you

You need to replace the diverter valve.
Check out this page (https://www.askmehelpdesk.com/plumbing/sink-sprayer-cant-find-how-get-diverter-valve-193179.html) for more info.

Good Luck,
WallyH