With OBD-II it makes it easier to tune for injectors, cams, heads, etc. The issue right now is you do not have injectors, you are running a FMU, and boost a pump.
The second fuel pump is only on during +x amount of boost via a hobbs switch, if you run to big a fuel pump without your motor needing all the fuel, you heat the fuel needlessly, over work your fuel system needlessly, and cause blowback (causing fuel to find an escape route, weak seals, fuel cap, injectors, etc) If you run the inline system you don't have to tap the fuel tank to get to the intank, and it can easily be taken out of the line if needed for some reason. As in my inline pump picture you can see I can skip the inline and return to stock by undoing two lines.
I do highly recommend the crane box, your link is the one I use, it can be returned to stock if ever needed, keeps the plugs firing and adds many options to your current setup. Do not delete your timing retard box unless you have someone tune your factory ECM to take timing out as your rpms build. Regardless of boost or not your motor advances timing with RPMS you do this on a SC motor without timing retard kiss that motor goodbye, unless running high octane fuel on low boost...110 octane on no more then 6-8psi. Check the forums I think total timing is 24* where base timing with spout connector out is 10* advancing your base timing makes great low power and only slightly changes your total timing, which can only be adjusted via a tuner or sorts.
Injectors come in sizes of 19, 21, 24, 30, 36, etc I know up to 80s have been run and tuned to idle well... max on your setup would be 30s. Your SC isn't going to create any more boost then what is showing on your gauge without better flowing heads and manifolds (lower and upper) you may squeeze out 9psi with alum. heads and a ported polished manifold setup.
Your fuel levels if not dropping off are good with your current boost levels.
Opinion Time: If you have a dead spot in power, it is your factory cam or factory torque convertor(TC), doing that...check out advancing your cam, or get a replacement, this is a hard choice check the forums and be honest with yourself about where you want the powerband then pick a cam. If the TC is the problem, talk to someone else, I like manuals.
Heads your current E7 heads could be swapped and net you a HUGE increase in power from idle to redline, I love AFR 185s they are great choice of torque and HP, they are alum. so your motor can take alittle more timing creating more power....BUT they cost a few bucks, again if you do heads check your combustion chamber number to go with an aftermarket cam if you get one. There has been results of 50-70hp from idle to redline just by changing heads!
Intake your current setup is the factory truck intake for the 351, and it blows. you can get your lower ported and polished to give a few ponies but really not worth it, sorry.
Overall, do the fuel and spark upgrades I recommend, find some empty road, adjust timing run it, adjust timing run it, retard boost, adjust timing run it, play with this combo until you find your happy spot. I was at a dyno tune with a KB SC and saw 40hp come from just adjusting timing and boost retard! Once you find your happy power spot then you have the next issue your Tranny!