There's 2 shift overrides on Ford.
1) is to turn the key away the lock position, but not ON. This should let you shift into neutral, where you can then turn the ignition further and start the truck.
2) there's a mechanical overide inside the steering column (below the turn signal switch) but you have to take the shroud apart to reach it.
I agree with the comment on the high mount stop light.... This is the one that triggers the interlock.
Also do you use your parking brake? If the truck rolls hard enough against the park pawl, it might not be an interlock issue, and you just need to relieve driveline pressure.