CM2250 Poor fuel mileage

[Truckdriven]

I recently put a truck on the road that had been parked for 2 to 3 years before I bought it and now has terrible fuel economy in the 4.5 mpg range. Truck is a 2012 Kenworth W900B Vin 1XKWD49X5CJ324795 Engine serial # 79502726 CPL 3719 18 spd 11r24.5 tires 3.70 rears 633K miles 24,700hrs we pull a 53-foot livestock trailer with a good mix of secondary roads and Interstate running 50/50 loaded 80-85k and empty 33k lbs. Engine was stock until I got it and had it deman dated by R R on this forum and set 500hp 1800tq. One thing I question is the Boost pressure will be about 30 if I let it lug under 1500 rpm (not normal driving habit) and will drop quickly as soon as it's above 1500, about 25 at 1600 and 20 at 1800, is this normal??? Also greatly drops off in power above 1500 compared to our cm570 with same power settings.

Work done in the last 12k miles, vgt rebuilt, overhead set, fuel pump rebuild, new intercooler and all connector boots and clamps, new exhaust press sensor and tube (wasn't plugged), new imap sensor, barometric pressure sensor, fuel rail press sensor, fuel pump solenoid, rod and main bearing, oil pump jacked to 40ish PSI.

Injector leak down test was 900psi drop in a minute first time and 700 second time, 10k ago it was 340.

Yes I know it's aerodynamics don't do it any favors and I'm not looking for 9mpg but in comparison to friends doing the same work with long hood trucks they are 1.5 - 2 mpg ahead of me, even the old CAT guys all beat me and even the vgt deleted isx gets nearly 2 mpg better! (No I won't be doing that)

Could being parked so long have anything to do with it? Like the injectors getting slightly gummy and not functioning properly?? Is my oil pump set to high and adding to much load?? I've done what I know to do and nothing made any difference.