d16 turbo problem

would like a little help with recent problem with truck. 2007 d16 535hp. 2 weeks ago turbo stopped spooling up. took to dealer in new orleans area was told new turbo 6400.00 dollars. this didnt sound right to me so drove truck 900 miles mt back home to local shop who disassembled turbo to check vgt ring. vgt moving freely. decided to replace turbo actuator and boost sensor. picked up truck today and has exactly same problem. have engine code for air flow sensor. if bad can this stop turbo from developing boost? no other codes showing on dash. truck has run great working gas wells in pennsylvania until 2 months ago. repairs started and am now at about 15000.00 dollars in repairs. any help would be greatly appreciated