I just did the 5000 miles oil change. Couple days after I did a trip from GreenBay WI to Lacrosse WI, then Lacrosse WI to Minneapolis MN, back to Lacrosse, then to GreenBay. I notice there is a drop of Gas Milage. I use cruise control as soon as I am up on the highway.

GreenBay to Lacrosse - around 38, which I normally can do a 42 MPG (with 35 psi on my tires)
Outside temperature on that night was around 39F.
200 miles trip: around 80 miles on the highway driving around 70mph, and 120 miles of 2 lane local highway around 63mph

Lacrosse to Minneapolis, then back to lacrosse - unbelivable 35.7 MPG. I couldn't believe that. Total distance is around 300 miles The temperature showed 39F and my tired pressure was around 33psi. I was driving around 71 - 73 mph for the whole trip.

Lacrosse to GreenBay - around 40, with outside temperature around 45F. I inflated my tires alittle bit to 35 psi.

As winter is coming soon to GreenBay, i hesitate to inflate my tire pressure too high in order to optimize the traction in snowing condition

Any suggestion what I should do?