You didn't give us much to go on. Please elaborate if you have more details from either the shop or how it's running etc etc.

It is odd that you can shift it by selecting the gears, and it won't take care of itself in drive. Reason for that is the transmission is fully electronic for shifting and shift pressure. Whether you pull it down a gear or leave it in drive..it should be commanding the soleniods in nearly the same way. What happens when you select Drive...does it sit in third?