What's the GVW of both truck and trailer? Am willing to bet the truck will weigh in close to 8500 pounds or more. What is the truck itself (crew cab, 4x4, short box etc)? Think we will be better able to assist you once we know the details.
As for that year of Ford diesels, they had/used 6.4 International's. Memory doesn't serve me well w/ that motor, but do know it was better than the 6.0.
