Perhaps it's due to a 44.1/48 kHz mixup during conversion. Try switching sample rates (w/o resampling) and see if that makes it right. If not, you'd need to time stretch the entire file (assuming it's constant throughout). If you have a good ear, you can do this by trial and error. Otherwise, you can do an FFT analysis on pure tones (maybe if you have a good solid bass note somewhere) and tune using that.