Higher mileage 2006 F-150 ?

[Mustang1989]

I'm tired of having to throw lots of money at my '05 F250 every couple of months to keep it running, and since I rarely tow I'm thinking of selling it and getting a nice used F-150. I found a good deal on a 2006 F-150 crew cab FX4 automatic with the 5.4 liter. The problem is it has 139k miles. Now I haven't seen it yet, but should the mileage be enough to scare me off? What kind of life expectancy should one get with the 3 valve 5.4? Heck, if nothing else I can always throw in a rebuilt motor down the road. That's gotta be cheaper than keeping my F-250.