I don't think brand of oil matters, but I would found out what wieght he used, maybe he was running thicker oil. if it is still 5/30 like from the factory go with some thicker oil or just throw some oil treatment in it.

 

I could be that the Mobil 1 is a bit thinner. It coats well, but maybe the switch was good for better lubrication. That knock is normal at those miles.
My previous 2000 5.3L Silverado started doing that at 120,000mi. It still spun to 6200 rpms with no issues all the way to 150,000 miles when it was traded.
The only thing I noticed was that it consumed about 1.5 qts between my 4,000mi oil change intervals.
It will be fine. Which oil filter are you using?

Jim

 

drain a quart of oil and put a bottle of lucas oil stabilizer in there. it will make it quiet.

 

I don't know, man, when you start knocking in the bottom-end at the back of the motor...that doesn't sound normal! I HOPE I'm wrong.