high pyro temp/low boost/weak engine brake

[ILfarmer89]

New member, please bear with me, looking to glean the knowledge found here and get some help with a few issues I'm having with my ISX. So I recently purchased my first truck, bought it on auction. As far as the truck itself goes, it seems to be a good, southern truck with very little rust and well taken care of inside and out and spec'd the way I wanted. My plan is to use it during the off season of farming to do some local custom hauling. The truck has '06 model year of the CM870 ISX rated at 475hp. It came with documented overhaul and has less than 50,000 miles since the overhaul was completed. The issue I'm having is the pyro is running high, on flat ground, pulling a load at 65mph, the pyro reads 1000-1100. Along with that, the boost never builds up beyond 25-27psi and the engine brake on stage 3 is basically useless. There's no CEL on, oil pressure runs steady at 35psi and coolant temp rarely gets above 200. It does have an adjustable fuel pressure harness on it but as far as I can tell, that's about it. EGR is still on the truck and as far as I can tell, it hasn't been De-Mandated. I intend on inspecting this further to see if it actually has been De-mandated but was left on the motor for appearances sake. My gut is telling that it actually HAS BEEN De-Mandated and has a hack-n-slash "tune" in it that is what is causing my problems. Any insights into what would be causing my problems? Could it be something else beyond a bad tune causing the problems? Thank you all in advance for taking the time to help with this problem.