Hello and welcome to JA, there is a tsb (technical service bulletin) pertaining to your vehicle, I will attach it, but before we get into that, the RSC/ABS system does have the capability to retain diagnostic trouble codes, however when these are the fault of the inner circuitry of the abs module, the code will only be retrievable when the light is on, once the key has been turned off, the code will be lost, having said that, it may be a good idea to bring the code reader with you and hopefully you can catch it before you turn off the truck the next time the lights come on. This tsb is for an internal problem with the abs module which sounds like exactly what you have going on, but lets try to verify the code matches up with the one listed in the tsb before we replace the module. The programming of the module can only be done at a ford dealer, just to let you know ahead of time.
Some 2006 E-Series 350 extended body vehicles equipped with a 5.4L engine may exhibit a Roll Stability Control (RSC) indicator light on with diagnostic trouble code (DTC) C1288.
Follow the Service Procedure steps to correct the condition.