Your problem is in your first few sentences- - - -"Firestone"! I do warranty and damage claim inspections, and a huge number of my assignments involve claims against Bridgestone/Firestone stores. Find an old established independent alignment shop with someone there who knows enough about alignment theory to make your truck steer properly. Who did the installation of the new components? There are several possible ways to assemble things improperly that can cause the symptoms you're describing, but an experienced front end man should be able to spot that kind of thing right away. BTW, the "manager" (who is actually a salesman) is right about the camber adjustment procedure. That's the way I taught it for over 30 years.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!