I have been trying to get the answer to that question for two years. From what I have found out the motors are identical with identical performance but rated to different specs. I have not been able to find a copy of the rating specs without paying several hundred dollars to SAE and no-one has volunteered to get a copy for me. No dealers I have talked with are even aware of the different ratings and cannot explain it when I ask. They also cannot explain why the diesel has the same rating in both trucks if it is just a GVWR issue. To further confuse the issue, the same motor in the F150 gets a third set of ratings and again I am told that it is the same motor.
