bad mpg what to do?

I just bought a 2009 Freightliner columbia with detroit s60 13 sp 455 hp 3:55 ratio I drove about 872 miles loaded at 74000lbs gross filled up 193glns I averaged out 4.5 mpg. Truck feels lazy to pick up speed. Anybody thinks its better to crank up hp to 515? Or do tune up? It only has 500,000 miles you guys think I should cancel or replace my egr?

 

I was going 70-72 interstate I80 to i35 ll plain I do flat bed but I driven other trucks like cummins N-14 I would average 5.5 to 6.0 on that speed and much more power this truck feels lazy I step on the pedal and it picks up slowly never driven a truck that feels this weak. If I crank it up to 515 will I have a problem with the injectors or turbo? Will my mpg worsen or get better?

 

70-72 on plain road first time with detroit I use to drive cummins n-14 and Mercedes

 

Do you know how much it costs to raise up the horse power?

 

Just got the truck two weeks ago it has new air filter I bought it from arrow truck sales tire pressure at 100 on the drives 22.5 rim size on recaps for now