Try some Motor Oil Saver or ATP 205 Reseal in it and see if it cuts the consumption by seal leaks. Had them slow and stop oil loss on a couple vehicles. Are the rings gummed up possibly, try some Rislone or HPL oil cleaner for a oil change a see if that helps w stuck rings.
Had a trailblazer that I couldn't get the p0420 to go away, mechanic tested a couple things and was like oh nope it's the cat. Replaced the cat w oem and p0420 came back in 700miles. Switched oil to Maxline red bottle, put a bottle of atp 205 reseal in it and code went away by the end of the 5k oil change, kept up w Maxlife in the truck and never had code come back and oil consumption dropped to