You are not supposed to gap Platnium or Iridium plugs at all. The metal is only a coating, and easily damaged. No gapping or cleaning. Install the plug, or remove and discard..that's it.
Honestly, I'd return them for motorcraft copper plugs. The 5.0's seem to really love those plugs. The only benefit to platniums is longer replacement intervals. They actually have a higher resistance than copper plugs.
The coil does state the gap can be opened up. Even more reason to try that with plain copper plugs which have less resistance, and can be gapped.