Just bought first truck. Not sure if it's deleted

[rowdyplemc]

Just bought my first truck a 2012 T660 with a 2010 ISX15. chassis has 950xxx miles engine has 230xxx on overhaul with paperwork. Upon inspection of the truck before purchase there was a generic code on the dash. "DPF injector 1 no response". Online searches lead to "doser injector" being an issue however talking to the salesman at the dealership he informed me that the mechanic that he hires from the towns local shop informed him that it was actually the "doser valve" that was causing the code. I went ahead and purchased the truck and turned around the same day and purchased a doser valve from my local KW dealer. I had to drive the truck a total of about 350 miles to get home bobtailing. In this 350 miles the truck runs great I'm extremely happy with my purchase HOWEVER I have a little bit of a concern. The truck used absolutely zero DEF fluid on the trip. (Still haven't replaced doser valve because not sure if an issue is there or not or if I possibly have a deleted truck. Truck is parked for now). The truck never went into derate or showed signs of derate. The turbo has a very slight whistle at idle that I'm not used to hearing in previous trucks I've driven. Online forums suggest this means the EGR is blocked off and causing the turbo to rotate slightly faster but not quite spool. So my question ultimately is do these signs lead you to believe it has been deleted? If not why did the truck not derate in that 350 miles if the doser valve truly is faulty. Trip was a mixture of city and hwy miles. I have the doser valve on hand ready to replace but am worried if I go ahead and replace it and the truck is deleted then I wasted $550 for a paperweight. Thank you