ISX cm2350 low. power/poor. Fuel milage.

[DPS567180]

Okay I'm really frustrated now. I've been dealing with low power going uphills no matter what the weight is and my fuel mileage is in the toilet. What I've done so far:
Egr tuneup cleaned egr valve/cross over tube All new sensors seals, gaskets and clamps. The only thing I did not touch was the EGR cooler which I plan on doing when I get back home next week. I plan on cleaning it and putting new gaskets in clamps on. I also hear a whistling noise more like air coming through a small hole. I pressure tested my intake side of the engine and no leaks. Boost is at 30 when climbing and it holds on a long pull just no power even when my trailer is empty. I'm really trying to avoid going to the dealer especially my local dealership they are horrible. Any suggestions would be great.
Oh I almost forgot exhaust manifold gaskets are new as well. No codes are popping up. I do have Insite but I wouldn't know what to look for on there so any help would be appreciated. Truck is 2015 Prostar