Without doing some investigating with a scan tool to watch trans data I cant be of too much help, but the common causes here are a bad fluid pressure switch manifold or wiring and may require dropping the trans down to remove the side cover to replace the pressure switch manifold if it is at fault. He could try unplugging and plugging back in the trans connector to see if that helps. If you or he has a scan tool or can borrow one it will help out, then you can verify that the pcm is seeing the correct gear internally that matches the shifter.
