....... I don't buy the urban legends about Pennzoil=sludge. Maybe that was true in 1950.... But that was a long time ago.
When I bought my F-150 new back in 1991, the salesman gave me a pamphlet, after I paid him and he kicked me to the curb with the keys. All with a smile on his face. It stated that Ford did not want it's customers to use Pennzoil in it's cars, because it contained too much paraffin.
I had heard that before from other sources as well. (Not that it makes it any more true). So I never used it. But that was a long time ago, and before synthetic oils became as popular, or as cheap as they are now.
So for years I used Castrol GTX. Mostly because I was a great admirer of John Force's dirty driving suits. Then I switched to Mobil 1 High Mileage 10W-40, and never looked back. To this day I have no idea if Pennzoil would have either damaged my engine, or turned it into a giant 2 wheel drive candle.