About sound - it can be transmitted through air and/or conducted through structure. Airborne noise can either be absorbed (eaten) or diffused (spread around), conducted noise must be isolated.
Thinking about getting rid of noise with "just one product", is probably going to leave you upset at that product (no matter what you choose). You need to think of the whole system, and remember that sound treatments come at a cost of weight (and $$$). And, you need to know where the sound that bothers you is coming from before you can mitigate it properly.
An engine is going to make airborne noise from certain sources - diesel ping is best transmitted by thin metal or plastic items like valve covers and oil pans which pass sounds easier (they don't offer much resistance to being hit by soundwaves, unlike a cast-iron block does). Fan noise is the flow of air over various objects and the design of the fan blades themselves, using a fan with wider blades that gently pull and guide the air vs. slapping/cutting into it like aggressive narrow blades do will help there (but finding one of those may be a challenge). Belts are going to have a certain sound as they run, as will your accessories. Absorption and diffusion are how you kill that - something like dynamat and closed cell foam sandwich on the valve covers and oil pan will lower the resonant frequency of the items making converting more sound energy into miniscule amounts of heat as it's absorbed by the material. Whatever gets past that needs to be further absorbed or diffused by engine compartment insulation. More absorber material on the hood and firewall will keep that airborne noise from getting into the cab.
Intake and exhaust noise is going to be both radiated by the piping and piped to the pipe opening (like a trumpet). The muffler is supposed to take care of a good portion of the exhaust noise, but you may need to put an intake silencer to cut down the intake valve noise. The piping might also be a source of objectionable noise, so wrapping it with an absorptive insulating blanket would help.
Conducted noise from an engine if coming from the vibration of the block through any attaching devices (plumbing, wiring, mounts, shafts...). The transmission, transfer case, and differentials will all conduct noise to the chassis as well. For those, you need to isolate them from the rest of the structure using vibration isolators (engine mounts are a form of that).
Tire noise can be both airborne or conducted (through the suspension). Putting sound absorber material in the wheel wells will cut down on the airborne noise (it'll also probably get torn up by rocks etc thrown off the tires...). For this, as any sound engineer will tell you, the best way to reduce the sound is to not make it. The type of tire tread will greatly affect the sound generated, everyone likes the look of the HMMWV tire tread, so changing this is probably not an option.
My suggestion is to start out by figuring out what sound on your truck you don't like the most, then maybe return for more specific advice? If you don't know specifically what you want to fix you may never know when you've succeeded...
