I have a '04 Escalade with the 6.0 in it , a few days ago the "Low Oil Pressure" light and bell went spastic. Oil level good, so I changed oil and filter (3,200 miles on old oil) I didn't help. So I replaced the oil pressure sending unit, didn't help. Replaced the oil pump and pickup tube, same thing, low oil pressure. with cold engine temp pressure ran around 20 psi, then dropped down below 15 with warm engine, maybe 6 psi at idle (but NO lifter noise). Any recommendations on what the problem might be?