I would try the oil change trick like "mike the crock" did in post #16. If one of the bearings didn't look right, I would assume that the old owner didn't change the oil often enough. I would not run 15/40 oil in one of these motors, as there has been problems with rings sticking.

 

When you have the pan off, pull the pressure relief valve out of the oil pump, debur and shim it and see if that helps at all. Maybe you got unlucky on the pump and got one with a sticky pressure relief plunger and/or really weak spring.

 

You should NOT run 15-40 oil in these LS motors...