e99 with 6spd bad milage
 

My buddy just picked up an f250 e99 manual trans xcab shortbed truck.
It had set for about 1.5 years before he had the mechanic get it and check it out for a maine to pensylvania drive (600 miles) The oil was changed and new fuel filter as well. The truck drove down here flawlessly, however, it only had gotten about 6-8mpg. Needless to say that was an expensive trip. Before the trip we had put in some diesel klean and fresh diesel. Then the next tank we added DK again.
The truck has had about 4 tanks run through it, with DK in every tank. It starts better now(before it started a little slower) but its also getting a little warmer in the mornings.
I convinced my buddy to buy the mbrp 4" exhaust, riffraff hpx and riffraff frx. Truck has the stock ecu and no chip or programer in it. brakes are all brand new now (one rear caliper piston was hanging up a little, but the rotor never got that hot from dragging)

What other issues could be causing this truck to get 8mpg
i had thought injectors or the wg was leaking/staying open/ no boost (but id think it would smoke with no boost)
truck uses no oil, does not smoke any, brand new transmisson, clutch, pp, flywheel, brakes
did a pressure test, and the intercooler boots are fine and dont leak

no gauges on the truck not sure of exact boost pressure

any help would be great guys...thanks

up pipes
 

Did you take a look at the up pipes for soot, that is the first thing that comes to mind. Clogged ebpv tube/valve maybe?

truck has good pep. doesnt sound like the ebpv is closed, and no check engine light on.

I have not checked to see if the uppipes are leaking, we will check that this weekend when we do the ccv mod.

I would think that if the truck isnt boosting correctly that it would smoke because it wasnt getting enough air. Truck is clean out the tailpipe