mine had a similar problem when i would try and cruise along in 5th and try and accelarate it would get to bout 90 then struggle and to get past it and the boost would drop to bout 4psi, i could get over 90 if i took it past in 4th then change gear but the boost always dropped off, my ecu isn't chipped, it has only been remapped, not to worry now tho the oil pump failed and bottom end went so doin a full rebuild slowly, but would like to know what you find out

rich