Cummins ixs 15 code

[Mishasvp]

Got 2014 Volvo with Cummins isx15 cm2350.. purchased truck not to long ago. Truck has 475 hp tune done by dealer. But truck does pull and on slight hills it looses rmps and boost. So far replaced throttle valve and checked for boost leaks. One time got a code spn 1239 fmi 16. But its not active anymore. Could it be injectors? Truck has only 420000 miles on it. Any help would be appreciated. Thank you.