if it isnt burning off the cat, & it is coming from the exhaust, it sounds like worn valve guides, & or seals. get a friend or someone to follow you & verify.
when you drive the oil is in the top of engine, then stop at a stoplight for a couple minutes, the oil seeps around the guides due to a higher vacuum at idle, & as you accelerate it will burn the oil that seeped. I have owned several vehicles that did that, usually you can get by replacing just the seals & can do that with engine in the vehicle in most vehicles.
also has engine ever been overheated? ever? a overheat will cause the seals to harden & then start breaking away & then this willl occur.
Randy