about 2 weeks ago i had a sudden loss of power. no turbo.. i got a scan and came up with a bad MAF and engine code "17964, P1556 Turbo/supercharger boost sensor (A) circuit: control limit not reached.". after replacing the MAF, i gained more power but still cannot go faster than 80mph. very slow acceleration. also, turbo only whistles in first gear.. i tested the hoses and they are fine. does this sound like a bad n75? bad actuator? or what... any help would be great