I recently had to replace the aerator on my single lever, Delta kitchen faucet. The plastic internals at the faucet output would no longer stay inside the metal, threaded housing. I purchased a replacement internal 1.5 gpm aerator. Now, however, after turning the water off, the water from the faucet does not immediately stop. I have tried a full (externally threaded metal housing with 1.5 gpm internal) aerator, a 1.0 gpm complete aerator, and two other complete 1.5 gpm aerators (clear output and spray). Nothing seems to matter. Do you have any advice on what would suddenly be causing this condition?

Remove the aerator fron the spout. You will see a flow resister,(see image).
Pry it out and toss it. Open and close the faucet without the aerator. Work normal? Pressure builds up behind the flow resister and what you're seeing is the pressure bleeding off. Reinstall the aerator and test. Better now? Cheers, Tom