I have been told older truck diesel engines like mine were tuned down from the factory by Ford for lower horsepower & torque to prevent higher exhaust gas temperatures, which must be monitored with an additional EGT gauge if a tuner or chip is used.
In our case, our engine was manufactured by International. It is my understanding International used more horsepower and torque their engines, but that is what I have read in some forums; I do not know if it is true or not.
I hope to hear from some of you who use tuners/chips regarding reliability/drive-ability over the years of towing.