GMC R1500 Two Wheel Drive 5

GMC R1500 Two Wheel Drive 5.7 motor 700R4 Trans. Smog pump blows air to breather connection, Is this correct? Thought it took air from the breather to the exhaust manifold. Engine runs great if idle is aprox. 900 but dies otherwise at stops. Engine has 50000 on it but at lower idle than 900 oil pressure drops to lower than 30 and dies. Does the computer tell it to die at this pressure. Has TBI. Have replaced all sensors. Checked compression. Checked for all vacuum leaks. Replaced fuel pump and checked fuel lines regulator on TBI. Checks 11# overhauled TBI. Replaced Dist and coil and wires and plugs. All GM parts