20W50 is extremely heavy, I don't see why you would run it in any car.

Try some synthetic 5w40, see if that doesn't clear them up. I know Delvac 1 helped the lifters on my 603 a lot.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200