If you use some simple googlefoo on Ford electric steering, "how it works" and "problems", this issue doesn't come up. There ARE issues with other vehicle types (cars-SUVs) where the Ford EPAS electronics can fail due to excess heat and from faulty steering torque/angle sensors. In at least one case the steering is driven hard off-center by the failure causing an accident. My hypothesis for the posted problem, since it goes away almost immediately, is the steering angle /torque sensor (SAS) on the steering shaft is losing communication to/from the motor drive board mounted inside the case on the rack during the extreme high amplitude vibrations. Basically loose wire/connections, or another faulty SAS. It's the type of thing that will never show up on a scan tool or test drive unless the truck is subjected to the actual vibration scenario.