stock tune- but did you actually do the dpf delete within the tune? i had a guy bring me a truck yesterday that her just cut the dpf off and was wondering why he was getting engine codes and a reduced power mode
make sure your dpf is turned off within the tune and adjust MIL to coenside.
also,,,had a customer that kept throwing reduced power and after trial and error last resort type thing i checked his airbox,,,dirty as a MF so i cleaned it and voila....problem fixed!
hope some of this helped...can you tell us about what time/ symptoms of it going into limp mode? Is this at WOT or just cruising along normal?