The 2.5's with automatics came with 3.73's, so it's a good chance that axle wasn't abused. That's one easy bolt in replacement. Try to get the axle with the ebrake cables still installed. Makes it much easier and much less labor.
Most are trying to give away D35's, so I hope you are getting it for a good price. Keep your old axle shafts as spares and get pics of the parts your mechanic says is toast.