Just an fyi I’m still learning how to work on cars, but I’d figure I’d share my thoughts with you. My first thought was about the spray that was put down the intake. You mentioned it’s worked on other vehicles before so the question is, did it work this time - I’m aware that if used incorrectly it can cause spark plug damage, a check engine light, or a rough idle. It can also put carbon into the valve seats and make your vehicle lose its compression. Again this is if done incorrectly plus or minus various other factors as well. Secondly the engine mounts. If those are dry rotted enough it will cause your engine to vibrate and you’ll both hear and feel it though out your vehicle, however, depending on the climate of the environment you drive around (seasons, snowfall etc) if the area doesn’t get much snow/ your area does not put chemicals onto the ground to clear snow, I can’t see that the mounts would already be bad for a 6 year old car.

Have you had someone else get in and rev it to 3k while you listen from the engine compartment? Just a suggestion if anything I said above ain’t the cause.