Joe decides one day to trade in his 2005 Dodge Ram Cummins for a sweet new ride. Joe enjoyed the power and performance gains his tuner gave him for many years. The hardware Joe had put away to tune his truck was lost in his last divorce.
Lets take a ride to the imaginary used car lot for a bit. John the salesman takes the truck in on trade. The dash has no warning lights and the truck runs very well, should have no problem selling it.
Now you are you, and you find a truck that fits your needs perfectly. It has a fair price and you buy the truck.
Some time after, an engine light appears and generates codes that no one can seem to decipher. Any knowledgeable shop would probably see the weird malfunction and recommend a replacement PCM. This will fix the problem when the new PCM has been programmed with stock software. No one will know why it’s fixed, just that it is.
You pick the truck up and feel the truck isn’t right, its now under powered and gets poor fuel mileage. An automatic response to a new symptom occurring after an official repair is to blame the shop for doing something wrong. A return trip will prove nothing out of the ordinary exists and are sent back on your way.
This mysterious dragon syndrome occurs often, and the correct response is to tune over the corrupt tune file, or re-flash the PCM to stock and then tune over the stock file.