2002 with 3.5 oil usage

I have a the 3.5 bought at 137,000 miles found out at 170,000 miles that it had the wrong oil dip stick. I always changed the oil and always check oil so when I checked the oil I added to full. Then one oil change checked and low so thought I was off on my count so added a qt. but after 500 miles it bothered me so changed oil again and confirmed dip stick was bad. The car is using oil surprise surprise, but it runs great, idles great, no knocks, no leaks at all and doesn't smoke at all (cats must be working good). I'm going to try some engine flush (AMSOIL) because the oil does get dirty fast. Just looking for any other any thoughts like chances of stuck oil piston rings or valve guide seals. EGR system? Uses a quart a week about 100 miles.
Just looking for any suggestions other than junk it. Car is in great shape and everything works great and love the power.