Delta Michael Graves Faucet slow to turn off

[ShouldaPaid]

I write this desperately seeking your help. I have a Delta Single Handle Kitchen Faucet from the Michael Graves collection (187-WF). Here is the link to the parts:

https://media.deltafaucet.com/PartsDiagram/Models_186_187.pdf

It was working perfectly. My problem started when I installed an under the cabinet water filter. As soon as I installed it, the sink went from immediate shut-off to a 3-second shut off. So when I went to shut it off, instead of just going instantly off, it kind of petered off. After about 2 weeks of this I decided that this was more annoying than having dirty water, so I removed the filter and hooked it back up the way I found it. But then, IT WAS STILL SLOW! I have no idea why that it is? But then I got to thinking, when I first installed the water filter, I ran it for 10 minutes or so because with water filters, the excess black carbon needs to be flushed before using it. I figured maybe all that black dust that went through the lines might have gummed up the plumbing.

Since then, it's been a neverending quest to return the sink back to its originaly "instant-off" glory. I have replaced the following pieces:
RP4993 - seats and springs
RP25 - O-rings
RP6052 - Gasket
RP37033 - Spout Hose
RP13938 - O-rings
RP37021 - O-ring (just one of these, I couldn't get to the top one)
RP40372 - A $72 piece, didn't fix anything.

Nothing fixed it, if anything, after all these replacements, it's still petering off even slower rather than giving us an "instant-off." If I didn't list a part it means I didn't replace it (yet). Next on the list is RP70 (ball assembly) and RP320 (diverter assembly), even though I did dismantle those and clean them thoroughly, that didn't help.

I will also note one thing, I disconnected only the spout-side of the spout house (RP37033) and ran the spout house into a bucket while the water was on. Turning off the water at that point gave me an "instant off" which suggests to me that the problem lies after the spout house on the way to the faucet. I just don't know what else to fix.

Am I missing something obvious?

I don't want to buy a new faucet, I want to solve this problem.

Please help.
Many thanks in advance.

 

[ShouldaPaid]

Too long, didn't read?

Instead of having immediate shut-off, the faucet takes 3-seconds to shut off. I have replaced RP4993, RP25, RP6052, RP37033, RP13938, RP37021, RP40372. Nothing has fixed it! I have not replaced RP70 or RP320 yet. help!

 

[TomFOhio]

There is a divertor under the spout. Try cleaning or replacing that. RP 320 on your parts breakdown.
Let us know what you find.

 

[ShouldaPaid]

There is a divertor under the spout. Try cleaning or replacing that. RP 320 on your parts breakdown.
Let us know what you find.

Thank you for your response.

Update: I went to buy the RP320 and they informed me that the part has been replaced with RP63136, so I bought that and replaced it. It was a bit hard to get into the whole, but eventually it snapped into place.

Didn't help. Still takes a few seconds to turn off! I don't know what else it could be!!

 

[TomFOhio]

Sorry that the divertor didn't work. You probably already did this but turn the faucet on and
run the spray hose on and off a couple times and see if that helps. If not call Delta tec and see
if they can give you any help.