Your local chevy dealership carries the best top end cleaner. (personal opinion)
I think it is actually called top engine cleaner.
It has the proper instructions on the bottle.

It’s been a while since I used it but this is what I remember.
Basically you unhook a vacuum hose, it gets sucked into your engine until it stalls.
You let it sit for like 30 minutes.
Then you drive it fast and hard, it smokes so bad you think you F’d your engine up!
But just after a little while you would swear you had a tune up.