My Ford manual states during trailer pulling or heavy load conditions allow the engine to idle 7-10 minutes for cool down to prevent carbon forming in the turbo bearings from over heated oil due to excessive heat. I also have a EGT indicator on the turbo outlet and I let it cool to 225-250 degrees before turning off the engine.
Charlie
2001 F-250 Lariat SC 4x2 LB 7.3L PSD
BD Power ECM 80 HP Performance Chip
BD Power X-Monitor LED Digital Gauges
Firestone Ride-Rite Air Bags
2005 3295RK