I have 2015 Ford F350 with 6.7 Powerstroke and in the Diesel Supplement owners manual under Switching off the engine: "To prolong engine life (especially after extended high speed, high ambient temperature or high GVW/GCVW operation such as heavy loads or heavy trailers) it is recommended that a hot engine be idled for 3-5 minutes. This allows the turbocharged engine to cool down."
If it good enough for Ford to document it in the owners manual, it good enough for me, especially while still under engine warranty.