Are you comparing your numbers on snow tires versus all season or summer? Snow or Winter tires get significantly worse gas mileage than all seasons or summer tires. This could be the difference you're seeing.

Also - fuel system cleaners arent all created equal. Check out BG 44K @ bgprod.com. Even Techron cant come close. And it WILL help with your MPG - you don't have to go on blind faith that it's actually doing something in there.

Edit - if you're using Sunoco to get the 94, chances are, the gas is blended with Ethanol. I don't know of any Sunoco that doesn't blend. This will result in a 20% hit in your MPG. And if I recall correctly, pretty much every station in GTA blends. You'll have to do some digging to find a 'brand' station that doesn't. In the states, I was lucky enough to find a Shell that doesn't blend about 8mins from home.

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2006 X5 3.0L - Schwarz Black/Truffle Brown
Stock
But I keep it clean