2005 WS 4900 550hp C15 low power issue

Hello everyone, new to this forum and hoping someone can help me out on here.

My truck is a 2005 Western Star 4900 C15 ACERT BXS rerated to 550hp with an 18sp Eaton Autoshift (clutch pedal version) 4.30 rearends and 11r24.5's. Lately this thing has been an absolute pooch...empty I can barely gain speed and hills I lose speed, loaded is obviously worse. I've had this truck to 2 shops including CAT and the Western Star dealer with no obvious finds. Boost is reading 45ish running down the highway, CAT says fuel pressure is good, air filters are new as well as fuel filters each oil change (10k miles), overhead was ran 60k miles ago, no boost leaks, CAC brand new 2 months ago. I'm stumped...I feel like this heavy haul truck should be walking everyone on the road but instead it can't get out of its own way and gets passed by swift trucks.

Anyone who can chime in would be very much appreciated, thanks in advance!