Engine surging going down a grade then throttle response gone and then derate code

2016 389 ISX 600
I have an issue after climbing a grade some times but not all the time. If i'm pulling a grade hard and after I start coming down with or without the engine brake the throttle loses response and the engine starts surging and flashes a 25% derate warning. I can either stop and restart the engine or hold the throttle down and the surges will become larger and then slowly return to normal operation. I'm going to replace the IMAP, Delta P, EGR psi switch (?) next to the Delta and the sensor (?) on the elbow after the EGR vale cross over tube. I just had the DPF & SCR filters serviced and change the PSI differential sensor down there but no luck runs stronger but still derate and surges at times. ANY thoughts??? One last thing the dealer wants to run scan, also thinks it has some to do with wiring from after treatment to Throttle Position Switch.

 

Ya your right . All those sensors were under a 500 bucks and I changed them out after I had the DPF and SCR filters were recently cleaned . Anyway the original problem turned out to be a leaking injector losing prime. The engine had dropped a liner about 50k ago at that time I had a premium rebuilt (in frame) at the Pete dealership at that time I also had them install new a head, new Con rods, and new injectors instead of re-manufactured parts. So the last thing I was thinking was a injector failing at 50k. It all turned out to be covered by warranty. Hey thanks for the response and your right would have been a quicker and painless to take it to a dealer. After dropping almost 35k on a in-frame you get a little gun shy about just taking it to a dealer. LOL