I think you got a good deal on the truck. If it was me, I'd be runnign the thinner oil and changing it regularly. You want it getting to all the nooks and crannies in that engine.
2012 F150 SuperCrew EcoBoost 4x4 XLT/XTR 145" WB 3.31 Axle - GONE
Five other ford trucks - all gone
Now rolling in a 2010 EconoBox Recession Fighter and a three letter tow rig