CAR COLD SHIFTS INTO GEAR

That sounds like an electronics problem.
Go have the trouble codes pulled. Any Advance Auto or Auto Zone will do this for free.

Have the transmission range sensor checked

You may have a problem with the torque converter. You should take it to a tranmission repair facility, don't go to AAMCO as they overcharge, but do go to a transmission facility as standard repair shops don't have the necassary tools to test and fix automatic transmissions. As ras said, the scanner may not pick up the range sensor if it requires a special scanner or a higher quality one or at least the experience of someone who deals with automatic transmsissions. They are not easy to work on and the experience of someone who knows them wqell is necassary as well.