870 loss of power and bad fuel mileage

[Redland1]

I have a 2003 International 9900i with an 04’ 870.It feels sluggish compared to how it used to run.It would pull 103-115k easily.But now 80k feels like it’s struggling.In the low end it’s really sluggish to get going and I have a good puff of black smile from the exhaust when climbing hills from a dead stop which it did not do before.At best it was a slight haze.I pressure tested the CAC in December and sprayed with soap.Found a couple of leaks at the boots but sealed them.Truck has always had an intake manifold pressure sensor circuit voltage below normal and or shorter to low source.Have changed the sensor and still the same.Even with that I was able to get 6.5mpg pulling a step deck.When I switched to frac sand pulling 103k it dropped to 5.5MPG but it was to be expected with the difference in weight.After a few months I got a code for EGR circuit short and a derate so instead of figuring out why it shorted I deleted it and the derate went away.Fuel mileage dropped to 4-4.5 pulling the same loads.

With the different voltage below normal or shorted to low source I’m wondering if I have a bad harness.Also wondering if the turbo or controller is bad with the extra smoke I’m getting.