So my 94 b4000 just recently started burning a noticeable amount of oil. Its running about a quart every 750 miles whereas i couldn't notice anything before. As for the oil i was previously using supertech 5w30 full synthetic high milage before and tried some 15w40 hdeo with some 5w20 since its winter (about a 4:1 mixture). Since i noticed it started burning that oil i did a change with some harvest king conventional 10w30 and the burning continues. Is it time to chastise it to a diet of 20w50 high milage or are there some more intermediate steps (pcv valve) that i should take in the meantime?