I checked our the SBCC website and methinks their stuff is mostly for show, not for any actual better performance.
Stock F350 calipers have dual 59.944 pistons= 225.8cm^2
SBCC calipers have triple 45mm pistons = 190.8cm^2 (opposing pistons don't add more force, just removes requirement for a floating caliper)
That means the SBCC calipers will have about 16% less clamping force on the pads. Now, that deficiency can be overcome with more swept area, but SBCC does not list that spec that I could find. Also, the SBCC calipers are Aluminum, which will deflect more under braking, making pedal feel softer. This can be overcome by making the calipers physically larger, but I don't think there is any space. The Ford calipers barely fit in a 17" wheel, and I do not see a note that larger wheels are required.
The recommendation for cross-drilled rotors on a 10,000 pound rig makes me even more suspicious they actually have no idea how to design a robust braking system. Cross-drilled rotors will not handle the thermal stresses of dissipating that much energy. They have their place, a large van is not one of them. FWIW - I did try them on my van. I thought I could make them work by having them cryo treated. Nope. In less than 6-months they cracked all the way through in multiple places. Here are pics of my cracked slotted/drilled rotors.
Notice the amount of surface checkering/cracking. This is the problem was was trying to correct by going with slots and holes. This was on the stock size rotors BTW. Obviously, it didn't fix the surface cracking problem, and only added more problems. The ulitimate solution was bigger rotors for better heat dissipation. Luckily, Ford discovered this also and made this an upgrade for '08+ vans. So I simply put in a new axle. Your 4wd F-series brakes are still slightly bigger than the stock 2wd '08+ E-series brakes.
A full fluid flush is a good place to start. But your driving style description, combined with your symptoms, really makes me think you just need to bed the brakes in, as described in my link above. It works! These vans have a high-temp fiction compound, so doing this periodically will give you better stoping power, and make your rotors last longer. Under normal conditions, they probably never get hot enough to transfer material. My van is towing most of the time, so I effectively do this involuntarily. I just did my rear rotors after 120,000 miles. My front rotors have about 70,000 miles and are barely worn (pads are ~50%).
Now if you try this, and you still can't lockup your brakes, then an easier and cheaper brake upgrade is stepping up the master cylinder. If you aren't smoking your brakes when coming down passes, or after a few hard stops, you really don't need bigger brakes. And if you can lock-up your tires (even with ABS you'll get a good initial chirp/squeal until it kicks in), then you are traction limited, and not brake limited so more braking power won't actually help stopping distance at all.