There is a chance that the service writer could be correct then, but I had
no idea that the '07 F150 was a fly-by-wire. If it is even remotely
convenient, take your truck to a different dealership.

I don't know how a fly-by-wire brake system works, and there is a chance
that a sinking pedal is normal. But I also try to stay on top of this sort
of thing, and putting a fly-by-wire system in anything other than a luxury
or luxury sports car is beyond where I thought the technology had gotten to.
These systems (fly-by-wire) are generally held to high-end models where
space is at a premium. BMW has a few fly-by-wire models, but they do it
because they found it easier than the mechanical linkage that they would
need to employ otherwise.

I'm not trumpeting BMW, nor neglecting others, but I can't foresee the
reasons why a Ford F150 would be fitted with fly-by-wire, especially on the
braking system. Even BMWs fly-by-wire system is on the gas pedal not the
brake. I do not recall any instance where fly-by-wire was used on a
passenger car brake system. I'm not suggesting it is not feasable -- they
use fly-by-wire brakes on airplanes, and have for a long time -- but I've
not heard of them using it on a passenger car or light duty truck.

PS
I've read reports that people are not getting used to fly-by-wire gas pedals
very well. They (the fly-by-wire systems) seem to have a different feel that
people are not comfortable with.