Ditty,
It sounds like you are saying that the HPOP recirculates it's oil, which is not the case. The hpop res., gets it's oil from the LPOP, if the HPOP is low, it's either because of, a failed, or failing IPR, leaking HPO lines, a failing LPOP (Good thing is, the truck will NOT run period, if the lpop fails), or, a low oil level. If you have visible oil on your dipstick, (even if it's in the add area)low oil level is not the problem.