The hyper-flash for turn signals only is not a bug, it's a feature. These "modern" vehicles don't use a conventional thermal flasher like more ancient cars did, but they are designed to respond in a similar manner.
Your truck's turn signals are activated by sending a very specific voltage from the multi-function switch to the instrument cluster, controlled by a specific resistor value. The instrument cluster then sends a J1850 message to the Front Control Module (FCM) and the FCM sends the trigger signal to the appropriate turn signal relay in the Power Distribution Center. The rate at which it flashes is controlled by the FCM to mimic the way a thermal flasher would hyper flash if there was lower than expected current heating up the thermal element (less heat = faster flashing). As it states in the owner's manual:
The arrow on either side of the instrument cluster flashes to indicate the direction of the turn, and proper operation of the front and rear turn signal lights. If a defective bulb or wiring circuit is detected for the turn signal system, the arrow indicators will flash at a faster rate. (Emphasis added.)
The designers tried really hard to make this "modern" truck act like the older vehicles that people were used to. Another related example (from the '04 FSM):
Each time the cluster detects a turn signal-on input from the turn signal switch circuitry of the multi-function switch on the turn/hazard switch mux circuit, the requested turn signal lamps and turn signal indicator will be flashed on and off, and an electromechanical relay soldered onto the cluster electronic circuit board will produce a clicking sound to emulate a conventional turn signal flasher. (Emphasis added.)
The FCM also controls the hazard warning lamps upon receiving a different J1850 bus message from the instrument cluster. Since the flashing rate of your hazard warning lights is normal, that suggests that the FCM does not take into account any detected "Lamp out" condition for that flashing function. It's all by design, rather than any "issue."
Out of curiosity, does your vehicle have the "Lamp Out" indicator lit?