4.5 quarts low? Holy hydrocarbon loss batman! I wouldn't think you could actually burn up that much oil, or if you did the engine would seize from lack of oil (only about 2 quarts left in the engine) and the remaining gunk left behind. In addition, it is really tough to burn up synthetic oil.
Could it be it was low when you started the trip, i.e., they did not put enough in there when they changed it? Seems to me that is is either leaking somewhere or enough wasn't put in in the first place.
I would say change the oil and make sure it is filled with the appropriate amount. Then monitor periodically.
If it is burning that much oil, I would be concerned that the cats may be getting damaged.
Could it be it was low when you started the trip, i.e., they did not put enough in there when they changed it? Seems to me that is is either leaking somewhere or enough wasn't put in in the first place.
I would say change the oil and make sure it is filled with the appropriate amount. Then monitor periodically.
If it is burning that much oil, I would be concerned that the cats may be getting damaged.