If it was not for bad luck I would have none at all!

I have always been told that Quaker State and Pennzoil both have the same additives in them that causes the nasty grey sludge. I can't be sure this is the case but it seems like that is what you have going on. Things being sludged up and preventing oil flow at low RPM is a classic sign of the Pennzoil sludge.

• Quaker State Corporation was created in 1931 by a consolidation of 19 companies.
• In 1998, Quaker State Corporation was merged with Pennzoil Company's marketing, manufacturing and fast oil change businesses to form Pennzoil-Quaker State® Company, a worldwide leader in consumer automotive products and vehicle care.
• In 2002, the acquisition of Pennzoil-Quaker State Company by Shell Oil Company, an affiliate of the Royal Dutch/Shell Group of Companies (now Royal Dutch Shell plc), was completed.
• In 2003, Pennzoil-Quaker State Company began doing business as SOPUS Products.

http://www.quakerstate.com/#/about-quaker-state