Series 60 power issues

Hey guys, going crazy here.. I am having power issues with my 08 series 60 14 liter. with 450,000 miles ..it has less power overall but especially in higher gears under a load. It just seems to run flat and falls on its face when I hit a hill. No funny noises or anything else that would throw up a red flag. If it had a small engine u would think it ran fine.. I had a CAC test, fuel pressure test, replaced all 6 injectors which helped a little bit. New EGR valve , new foot peedel kit, all filters changed, dyno said turbo is boosting fine. DPF Filter clean. Finally i had my power turned up from 455 to 515.. Have had 5 dyno's.. last dyno tech said it misses and slows down under a load. Which I can't feel it doing. It is just feels slow all around to me. I do feel it cut out for a second when I'm taking off from a stop but nothing more. I've been pulling my hair out trying to find my power issue. Please help

 

No gauges. It's been boosting between 35 and 40 psi acording to dyno...had all test done at the local freightliner.. i had injectors replaced by a detroit specialist shop.

 

Ok so now i have also replaced my turbo got new ECM harness to engine. And injector wiring harness. Power has not changed. At this point I'm thinking about taking it to a diesel performance shop. And/or getting and EGR delete kit....

 

Oh yeah im also putting in a 13 speed tranny. Had a 10. So I'm hoping the higher gear selection will help me pull hills a little better. At least keep from dropping rpms so much.