speed 6351,

I guess my thought would be it either leaked it or burned it. Have you given it a once over for leaks or did you see any smoke out the exhaust on your way to Reno. I don't think the problem can be pinned on the switch from regular to synthetic. A compression check might find a compromised cylinder...but that's a lot of oil to burn. I would think more along the lines of a leak.

Stuart