I only have a couple small things to add. With 90k miles I do not think your engine should be burning this much oil due to "wear". I think something else is going on - 1 quart in 3,000 miles would be more normal.
Can you say for sure if this is the first time you've had so much oil loss? I'm just throwing out that you could change your PCV valve since they are only like $5. I don't recall why, but I think I remember reading this can relate to oil loss/burn.
I was going to say if this is your first synthetic oil change, switch back to conventional you said it has always been on synthetic ...