6.0 Stumbles under load at low rpms and wide open throttle...ideas?

I've had an intermittent problem with my 05' 6.0 F250 for a while now. If I'm on the highway in high gear with the convertor locked in, cruising around 70mph at 2,000rpms.......if I smoothly roll onto the throttle so that the transmission doesn't kick down or unlock the convertor, as the boost starts to build......the motor starts to shutter/stumble and shake a little bit, it almost feels like a misfire. Now if I hit the pedal fast enough where the transmission will kick down a gear, it runs like a top...nice and smooth, full power with no issues.

The only time it does the stumble/shutter/misfire type thing is when I really bog it down, in high gear, with lots of boost (27psi).

I have no codes, HPOP pressures are good (580 idle/4,100 at wide open throttle). Fuel filters are all clean, and overall the truck runs like a top. I'm running a mild IDP towing tune.

I surfed some of the facebook 6.0 forums....and I had people telling me it was a bad HPOP, or ICP, or cracked head, or low fuel pressure, or bad fuel pump, bad torque convertor, or "it's normal to do that".....

The only thing that really makes sense to me is that it might be a weak injector that starts to crap out under big load.....does that sound plausible.

Any ideas on where to start troubleshooting this? No codes, so I'm starting from nothing. Maybe a cylinder contribution test?