Pick up tube could be clogged or its the oil pump. The only problem with it not pumping oil is it could have a spun bearing. The 6.0 I had a bad oil pump and it spun a main because of the oil pump. I had to get a new block because it tore up the main so bad. If you need it rebuilt I would go with Honeycutt in Columbia. He has great prices and does good work.
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