woah woah woahhh...... youve put slick 50 into a FRESHLY built engine?!?!?!?!?!?!?!?!?!??!?!?!?!?
fail!!! big time fail!
Aside from that stuff being crap at the best of times it will have prevented proper bedding in of the rings etc.
oh and ftr, thick oil gets upto pressure faster than thin oil