My 2000 Ford F350 (same thing) has the radiator internal cooler.
It also has the oem 9 plate external cooler.
When driving normal in 90 degrees it would be at 180.
When towing up a 10 mile grade 7-8% at almost full throttle 65mph it would reach 220 at the top of the hill.
Removed the 9 plate and installed a 2003-2006 6.0 liter trans cooler with 32 plates.....it was freakin huge!!
Now normal driving 140, towing up the same mountain with 7K trailer is 165-170 MAX.
I never had to back up a hill, but the cooler should handle it.
