Have you checked the Atessa fluid level? Inside the door rh boot - any atf will do but would be good to replace the lot with a quality synthetic atf.
Then try it in 2wd. Your trans mechanic is probably not aware that it is possible if done correctly - quoting from the manual:
Locate the "air bleed" wire behind the drivers kick panel, it's a plug with a single wire either side (usually green socket, white plug).
Disconnect it.
If you can't be bothered looking for and disconnecting the plug then remove the front driveshaft (4 bolts).