The IAH-ANC (or if you're doing the one-stop via SEA, IAH-SEA) segments can be very difficult to upgrade on at times. Both the seasonal IAH-ANC nonstop and year-round IAH-SEA-ANC flights get a lot of oil traffic between Houston and Alaska, and can have a bunch of elites on them. I have landed an ANC-SEA-IAH EUA upgrade as a silver before, so it is possible. However, that was nearly three years ago. These days I think I'd redeem miles for the upgrades on this one if you wanted to be sure and get it, because it's a long trip and a lot of people try to upgrade on it, and it's likely that there will be more elites on the flight than there are F seats available, depending on the day you're flying.