All depends on how long you like to keep your vehicles, and how hard you work them. FWIW I am a dealer, but I'm not going to tell someone they have to run AMSOIL or else...just not how I am and not how AMSOIL even wants their dealers to act. I see the benefit to running it and like the reduced maintenance schedule with increased equipment life.
It is possible to get OE for almost $20 a gallon. If you'd like to know how send me a PM and we can chat about it.
Signature Series is probably overkill for anyone with a truck, unless they never tow with it. I would recommend would be XL. It carries a 12k mile change interval no matter what you do with it, towing or DD.