I know this thread is old, but it's still relevant. I read the entire thread because Pennzoil Platinum High Mileage interested me.
I also watched multiple Youtube videos by Project Farm in which he said (paraphrasing) Amsoil Signature performed best of all oils he tested that year (2024 I think?) with Pennzoil Ultra Platinum a close 2nd, which would make PUP the best oil available from Walmart.
He went on to say all the other Pennzoil oils that he tested performed well, except Platinum. He was not inpressed with Platinum's performance in his various physical tests and he theorized it might be related to a weak additive package. He then show a VOA of PP and said it's additive package looked weak, but he like PUP's additive package better. He like all Pennzoil products (for their price, category) except PP.
Years ago I tried Pennzoil Platinum 5w30 in my 99 Jeep Cherokee. The oil pressure was lower than I was accustomed to from 5w30 Valvoline Synpower. It was obvious to me that PP was thinner than Synpower. PP claimed cSt looked normal, but IRL it was thin for a 5w30.
I realize this thread is about PP High Mileage, but it probably shares same base oil and additive package as PP, except hopefully the High Mileage version has more seal conditioners (especially considering how thin it seems to be).
I was considering Valvoline Extended Protection High Mileage vs Pennzoil Platinum High Mileage if I want a synthetic High Mileage (instead of a Blend High Mileage) because I had hopes that Pennzoil Platinum High Mileage would be much better than PP, but I'm giving up on that hope.
So far I have only read good things about Valvoline Extended Protection High Mileage. I'm also liking Maxlife High Mileage Blend too.