Any one running 275/55-20? If so what air pressure you guys running?

Is this a mpg question or a tread wear question?

Can't help you with that particular size but if this is a tread wear (tread life) question, I am running 35x12.50R18's and I am running 32psig in the rear and 35psig in the front in order to get full contact. I'm only including that as a reference as to some this would seem a bit low. I am also monitoring tread wear with a Fowler X-tread depth gauge so I can further refine my tire pressure for optimal wear (over thousands and thousands of miles of course).

If this is a tread life question I recommend that you apply a thick (wide) line of chalk or other powdery substance across the full width of your tread (do this for all tires as this will give you twice the results you need each time you move the vehicle...which will allow you to take more confidence in the patterns you are seeing) and then drive a few feet and inspect the contact pattern. Adjust air pressure, wipe the chalk off, and repeat as needed until you get full contact.

If you do the chalk test and the first test shows full contact then I suggest you increase the air pressure in your tires by 10-15psig and repeat the test. If you do that then you should see contact only in the center of your tread. Then reduce the pressure and repeat the test until you get full contact. If you don't start with partial contact you'll never know where that "sweet" spot is for perfect contact...in other words even if your first test shows full contact you might actually have less pressure than you need, which will wear the outsides of your tread faster than the center.