EscalatePriority is a ScripAction which is NOT intended to be called per transaction. It's intended to be called by an RT escalation daemon. (The daemon is called escalator).
EsclatePriority uses the following formula to change a ticket's priority:
Priority = Priority + (( FinalPriority - Priority ) / ( DueDate-Today))
Unless the duedate is past, in which case priority gets bumped straight to final priority.
In this way, priority is either increased or decreased toward the final priority as the ticket heads toward its due date.