two suggestions:
1. your Dr. P box is causing problems in the rail
2. your low-pressure fuel delivery system can't keep up with the Dr. P demand for fuel
some approaches to solving this:
a) check your fuel filter like mberry suggested. with high demand for fuel you could be on the hairy edge of the filter's performance.
b). Take the box off, then clear the code at Autozone (they will show you what button to push on their scanner), Then follow with a test like this:
1. run the truck stock for a day. be sure to test WOT, high speeds, all of that. if you get a code, then see your dealer. if no codes, proceed to the next step
2. put the box on. drive easy (no WOT high speeds). if you get a code then the box is causing problems. if you get no codes then proceed to the next step
3. got to WOT and/or high speed. if you get a code, then you are probably starving the low-pressure fuel system (you need a FASS or something equivalent).
I would not be surprised if you just need to upgrade your low-side fuel delivery.