So I took a round trip from Ohio to North Carolina over the weekend. This would give me a good test of mileage with GC. On long trips, small variations in driving habits are more likely to get averaged out. Well, I'm happy to report that I set a new record, 33.8 mpg. My previous high was 33.4 with Castrol GTX 5w-30. I rarely exceed 32 with Synpower 5w-40. I do this trip often so the route is pretty similar. One thing that concerns me though is that gas mileage seems to have jumped up since this trip. Even on a couple local trips today, I set new records for mileage (14 mile highway trips). For example, I have neve gotten over 30 mpg before (even with GC!) from work to home and this evening I got 32.2! I had the same experience with GTX and I attributed it to thinning. But I highly doubt that the GC could have thinned this much given that it has shown to hold viscosity well in UOAs and I only have 1300 miles on the oil. Can anything else cause the mpg to jump like this?