I hang out at f150forum.com a bit and that is a common problem to come up over there.
The 5.4 has a poor reliability reputation. The 2011 and newer 5.0 is a MUCH better engine in every way. Mine is a 2014 and it has more power than any truck I've ever owned, and gets the best fuel mileage than anything but the Tacoma. And the Tacoma only beats it by about 1 mpg. It isn't close to the performance of the old 302.
I don't want to start a pissing contest over the 2 engines. The 3.5 EB engine certainly puts out a lot of power at low rpm's and I've seen nothing to indicate it won't last as long as the 5.0 V8. It is a high performance engine that costs more up front,and it needs more expensive maintenance, and more often than the V8. Plus needs premium fuel to attain the advertised torque and HP numbers and doesn't get any better fuel mileage.
For what I do, and the light loads I tow the 5.0 made more sense to me. If I towed more weight, especially at altitude then I'd have bought the 3.5 and just paid for the performance.
