When people ask what to upgrade first, I usually recommend an aftermarket radio. Here’s a great article from Crutchfield Labs showing what difference aftermarket parts make for sound quality and overall loudness in an F150. It proves that an aftermarket deck is the best first upgrade. Combine it with a set of speakers and you’re even better off. Start adding amps and processors… well just check out the tests to see for yourself.
We worked on so many F150s where I worked because they sound like complete garbage. After seeing the stock sound curve, I see why. Just see what a difference upgrading your system makes.