Thanks for the links - helps frame my comments. I think you touched on the crux of the matter - they are "marketed" to what you want.....
If you need upgraded, aftermarket brake pads to provide a sense of security, then by all means purchase the aftermarket pads. IMHO, the OEM are as good if not better, and the costs are probably comparable. The choice of a rotor is as important, as aftermarket rotors are not all created equal (as Duane pointed out). Pads and rotors are integral on the performance of each other. That is the reasoning to recommend OEM rotors and pads - you know they are "matched" for each other, wrt quality to provide matched performance and longevity.
Both links you provided indicate the "towing" pads are high carbon - to help with preventing fade at higher operating temperatures - they do this by removing heat from the mating surface quickly (high carbon content) and more aggressive biting surface (how they lay down the metal in the pad manufacturing process, I think). High carbon pads do create higher levels of brake dust (ie black powder on rims).
Regarding your current set up, the Duragold pads may have ceramic? in them which does not dissipate heat well, allowing the mating surface to heat up, reducing friction forces at higher temps - ie fade. Slotted/drilled rotors do not help cool the mating face (that's the fins inside the mating surfaces of the rotors) Drilled/slotted rotors remove gas buildups at the mating surface, which also creates fade (the buildup of gases, that is). Can't comment any more on your existing setup.
Most importantly, the appropriate bedding in of the brakes will ensure good stopping power.
The installation cost is irrelevant in my opinion - I would pay top dollar for the best installer, for the best pads/rotors are poor performers if the installation is screwed up. Duallys are always complex jobs if you are replacing rotors - axle shafts need to be removed and reinserted, and the appropriate parts replaced - I personally have replaced all the seals, small clips, etc when I have done duallys.
Here is a link with some pictures for changing rear rotors on a dually. Interesting stuff.
Hope this helps some,
Brian