I kind of feel like I am beating a dead horse telling you the same thing over and over that you refuse to listen to, but here goes anway...
The reason we all like EFILive is because it is exactly NOT AT ALL like what you say. Sure, you can go to DuramaxTuner and buy a one-size-fits-"all" tune, but that is not what people on this forum do. The vendors here will work with your preferences and mods to create a tune unique to your truck and preferences (smoke, responsiveness, etc.). That's the point of having the ability to log, and work with your tuner. It isn't as necessary on a stock truck, since your truck is just like the other 100k guys' trucks, after all.
Second, the "dying out" at high speed could be from any number of things. It could be your rail pressure falling off, it could be defuel from a hurt trans, it could be a weird MAF limit, a limp mode, etc. The PPE tuner can't tell you any of that. You are throwing parts at the truck because you have no idea what is happening inside the engine. It might need a 2nd (or bigger) CP3, but it might well not.
Based on your claim that the trans is stock, I find draining the rail to be unlikely. You will nuke the stock trans in a spectacular fashion long before you run out of rail pressure, unless you happen to have one whipped CP3 on that truck, or a freak of a trans, or both.
Now, since you are throwing good money after bad and don't want to sell the dual CP3 setup, by all means, throw it on, and see if it gets better. If not, throw a lift pump on, and see if it gets better. If not, throw a 2nd turbo on and see if it gets better. :spit:
Or, you could use EFILive (or any logging tool) and determine what is causing your truck to fall off at high speeds, and fix the actual issue, not just guess at causes and throw parts at the truck. We are just trying to save you from unnecessary and complex mods that you don't need, and solve your root problem.
Finally, to reiterate what was stated earlier: a 2nd CP3 won't hurt the stock injectors or fuel system, so long as the dual-CP3 controller is working right. If that fails, then you have the potential to damage your fuel relief valve or even crack injector bodies, stock or not.