There are a few throttle enhancer devices on the market. As far as I can tell, they all operate on the principle of amplifying the signal from the pedal.
I've been running a Pedal Commander with the 3.5 NA motor in my XLT for a couple of months. The PC has a tremendous amount of settings, and it took me a while to find the one that suited me best, but I like it quite a lot. Essentially, you get more throttle response with less pedal push. The vehicle definitely feels more responsive and more quickly excitable. Some have said "just pushing the pedal faster will get you the same thing". In theory, I suppose that's true. In the real world, I haven't been able to replicate how the vehicle responds with the PC just by changing the way I use my right foot without the PC (test this many many times). Yes, some of the same responsiveness can be gained by a tune. That said, throttle enhancer devices are also compatible with tunes and offer the ability to fine-tune the pedal responsiveness to your personal preference. One thing I really like about the Pedal Commander is the ability to immediately switch settings or turn it off with just a couple pushes of the button. The two settings I use are "wife-in-car" and "wife-not-in-car".

It's also a super-easy and fast install/uninstall.
I have a Livernois tune on the way to me shortly. I intend to run both the tune and the Pedal Commander.