Oil type is PYB. Ok. If I'm reading you, your claiming no oil loss until near the end of an oil change, where it drops between 1/2-1qt. And you change your oil around 4k. My opinion on that is if you checked every 1k or so, you would see a more consistent drop. The loss of 1qt per 3k is approximately where I am (1qt per 4k). IMO it doesn't sound too bad. But it could be better. However if the driving pattern changes, say more highway and faster speeds at times, you could see a faster loss of oil, as I do.
In the morning after sitting all night have her start the car, you watch the tailpipe from behind when she does. Your looking for blue smoke right when it starts for a second or so. That would indicate the valve seals are on the way out. you will lose some oil there. Find out if its happening. The options are get the valve seals done, or try swelling them with High Mileage oil. Over time leaky valve seals will cause issues with the valve, use a fuel injector cleaner with PEA every other oil change to keep valves free of deposits.
If the Piston oil returns have become carbonized there's not a whole lot that can be done about it without a teardown. However if its just started burning oil, cleaning is possible. Once you've verified its not the valve seals, and the oil consumption is a recent event, there are a few ways to attempt an engine cleaning. A "drive with" additive combined with a full synthetic, or a "fast flush" used with PYB. I personally prefer using synthetic oil with a "drive with" engine cleaning additive because I'm paranoid what a cleaner does to the oil chemistry running in an engine over time.
Anyways here are the things I have tried that helped. I included your oil of choice with options:
- Change the PCV valve (use Toyota)
- Mobil 1 High Mileage/Kreen brew.
- Lubegard Engine Flush with PYB
Note: Prolonged oil consumption with this engine will rear its ugly head with a P0420 catalyst efficiency CEL. The efficiency programming is set to 95%, so at your mileage burning oil it can trip at any time. the sooner you try to resolve this the better.