The older diesels accepted a tuner very well, I have friends with 99 model f350s both have ran a tow tune for nearly 200k and were tuned around 100k. So that is a total of 300k on the engines with no failures. The one newer engine that really benifits from a tuner with delete capability it is the 6.4 psd. The emissions kill this engine and many fail with under 100k. If you run a (no power) tune that only deletes the problem equipment than the engine will last far longer. The post 2011 psd have much better emission systems and have no need for tuners with delete capabilities. I can tell you the 6.4 is very thirsty and the tuner if driven normal will add 3-4 mpg. (Hand calculated).