Dreaded D13 and air in fuel

Well here we go. I have air in fuel. Cant figure it out. A little background. FASS pump put on 3.5 years ago due to hard starting. New injectors and cups 3 years ago. Then liner failed and in-frame done 2 year ago with new head. Used same injectors and turbo (both less than or about a year old). Out of the gate, horrible fuel mileage and even worse power. At idle, the turbo was always screaming and under load at upper rpm you could hear turbo ‘surging’. Idle fuel usage was .9 to 1.0 gal per hour. Then one injector (#2) broke spring and was replace. In-frame shop blamed poor performance on turbo because used original and known coolant burned thru it. So i replace turbo with quality reman from volvo dealership and no change. So i checked for air in system and found it had it. So i replaced the filter housing. Still no change. So i replaced the cup AND injector on number 2 knowing he didnt change the cup. Cleaned hole good. Used proper volvo locktite on cup and graphite on injector. No change. So this time i bought two remans injectors and cups and decided to pull all of them and replace any that jump out obvious as wrecked with blowby. On pulling them (all but # 2 that i just replaced),i noticed a 4 of the five had signs of bouncing in the cup. So i did not replace any at this time. I blew out the holddown bolt holes and use graphite paste along with volvo install procedure. But this time, i went from 3 mpg to about 5 and idle went down to about .7-.8 gph. But power still not there, turbo still screams and surges under load. So three weeks ago did a six pack injectors. Im up to about 5-5.5 mpg and .6 - .8 gph at idle. Sometimes truck runs REAL smooth and has better power but is still missing alot. When empty climbing hills i should be accelerating on it barely holds or slows. So this weekend i isloated EVERTHING still getting tons of air. The only place i have not been able to isolate is between lift pump and filter housing and between filter housing and rear of block. I have clear lines from front of block to tank, plug in filter housing and anclear line on the original return so i can monitor returns from ‘bleeder’ valves in filter housing. When i turn on FASS pump without running engine, i have no air in either line as it pushes through system. And the primer is sealed tight (i plugged both bleeder holes and primed till i blew out filter seal. So it good before fingers start pointing. Plus entire system is always under pressure except tank to fass pump). But when i run engine, TONS of air in return line off front of block with no air in the bleeder line. This leads me to think there is nothing wring with pumps, filters or filter housing. I just pulled all injectors and zero signs of blowby. All have single concentric ring on the tip of the body where it mates to cup. Only thing i can think is head cracked in the fuel gallery. Any other thoughts? Be happy to send pics.