This is such a bad thread. The initial poster asks for advice, but also adds a statement about chemical cleaners being some kind of line that will not be crossed. Oh wait, there is also some statement about Pennzoil's ad conveying a cleanliness message that does not pass muster.
Then we move into the responses, which essentially argue one oil brand against the other.
Let's back up a second. Evern though this engine is a known "sludger," the OP tells us that the oil looks sludgy and drains slowly as a result. If this is true, not an exaggeration, a very serious situation is described, and this engine is not being lubed properly.
I think that some diagnostics and remediation are in order. The questions I would ask concern the underlying cause (PCV, Cooling system, lubrication problem in the past, excessive wear, exhaust blockage, emissions control failure etc.). If that can be determined, then fix and give some thought to whether the engine can be cleaned with oil changers or if it needs some physical disassembly.
For me, I might go with a short OCI with PYB, then another short OCI ended with a run through of Seafoam. After 1,000, do a change with the synthetic, and come back at 4000 miles and see where you are. You need to get that engine into a more normal operating condition.
Good luck