Rebuilt motor burning oil? Please help

[wdkwang]

My model is a '10 and had no burning oil issues before I had some warranty work done at a dealership this past July. Skipping the details, they told me they were going to give me a new motor since I had rod knock. They specifically said they ordered a new long block from Nissan, but screwed me and just opened up my motor and basically rebuilt it. I know this because the same stains that were on my motor before was still there after I got my car back.
Sometime in November, I did my routine Redline oil change in the driveway and noticed that only 3 quarts drained out. This freaked me out. I don't know if the technician didn't put enough oil or if that much oil has been burnt. So, I filled up a little more than 5.25 quarts, maybe 5.5. It read a little below the "H" on the dipstick. Note, this was in about 60F weather.
So tonight, I was checking my power steering fluid and it was reading noticeably below the Cold Min. which is probably due to the 18F weather out right now, fluid is still clear, and it's not leaking so that's probably not much of a problem (I haven't changed it since I got the car). I checked the oil dipstick after and it read very close to the "L" symbol. I then had my second freak out. I drove around for 20 minutes until the oil temp. read 200F. Parked in the driveway and the level read in the middle of the L and H.
Now my question is, is my motor actually burning oil and is in need of a real motor swap from Nissan? Or, is it burning oil because it's a rebuilt motor. I've read that new motors burn a little oil in the beginning, but does a rebuilt motor do the same? And if it does, how long is this supposed to persist for?
I am so worried right now, and feeling very reluctant to possibly go through the whole ordeal with trying to get warranty work done again.
Note: I got my car back with about 23,500 miles on the odomotor. It's now reading just below 30,000.
Thank you to whoever read through all of that.