Re-recording as sonnykeyes recommended is going to give you the best sounding recording.
I've only played around with the Time and Pitch Factory, but you can try the following:
1. Duplicate the track and copy the audio file onto it.
2. Mute the original track. You don't have to, but I would hide it. 'H'
3. Trim a section of the audio file, e.g. a complete phrase. I'm bar/beat oriented, so maybe a phrase that's about 2 bars long. Use the Marque tool to make your selection, then click Control-C to trim away audio on either side of this selection. The point is you want a small bit of audio to experiment with versus 60-90 minutes worth or whatever.
4. Double click on the remaining audio file to open it in the Sample editor.
5. In the sample editor, open Factory>Time and Pitch Machine. You'll see a Tempo selection with Original and Destination areas.
In the attachment you'll see that I changed the Destination Tempo from 120 to 100 bpm. Maybe you're working with SMPTE (hours: minutes: seconds: frames) so adjust the Destination setting according.
I'm also using isotope Radius. If you don't have that, you'll have to choose one of the algorithms supplied by Logic. Maybe someone else will chime in here, but you could try Universal or maybe Monophonic.
In the Pitch section at the bottom, leave Transposition and Harmonic Shift set at 0.
Make several copies of this trimmed bit of audio in step. Put each on on a separate track. Test out a Tempo change. Then go to the next track, try a different setting until to achieve a tempo and voice quality that is acceptable.
Have fun experimenting.