Oil Pressure Problem 04 Avalanche
 

Hello everyone,
I have a 2004 Chevy Avalanche with the 5.3L, is has 158,000 miles on it and recently I have done a bunch of work, but keep getting a low oil pressure warning. Recently just got done doing the oil pick up tube (replaced) and the oil pump and a while ago I replaced the oil pressure sensors and still have low oil pressure most I can do is at about 3-5k RPM it gets up to 20Psi. Does anyone have any suggestions that might help me fix this issue?
many thanks.