Internal Oil Leak

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I have an early model 99 7.3, and I have run into quite a large problem. Driving home from work one day at -45 degrees Ferenheit, my oil pressure guage dropped and the oil light came on. I thought that it must of been the oil getting thick, the next day I changed the oil, the oil that I drained from the pan was yellow like it had condensation or some sort of moisture, and possibly air. I replaced the oil and this didnt change anything, today I discovered there was no base oil pressure, so I checked the pump, and the pump met specifications, I checked the pressure relief valve in the oil filter housing, jacked the back of the truck up so the oil was in the front of the pan to check the pickup tube for a crack, this didnt fix it, I replaced a leaking turbo, checked the oil plugs behind the rear cover. None of these things have restored base oil pressure, the truck will run, but runs terribly. any suggestions?