[atertan]

I crossed 3000 miles on my 2010 terrain about a week ago and got an almost immediate boost in MPG of 4-6. I used to get 12-14 in town and now get 18-22. seems crazy but have verified with new tanks of gas. seems strange right.

 

[NoobNox]

Not strange at all...most engines increase gas mileage/power after they are broken in. It will eventually reach a peak and stay there for a couple years before gradually slding back the other way. However, 3k isn't really fully broken in so you may see another small increase @10k.

 

[RIT333]

I crossed 3000 miles on my 2010 terrain about a week ago and got an almost immediate boost in MPG of 4-6. I used to get 12-14 in town and now get 18-22. seems crazy but have verified with new tanks of gas. seems strange right.

If you were only getting 12-14 in town, maybe you lost your lead-foot at 3K miles. Did you buy new shoes ? A step change of ~30% increase in MPG sounds like more than just engine break-in - are you sure you didn't alter your driving style ?