2000 galant trans problems

my son has a 2000 galant, v6, auto trans. he was on freeway and had to brake very hard because of driver in front of him. after work he noticed the trans slipping in 2nd & 3rd. a few days later when he moved from park to drive the idle went way up and started rolling forward on it's own (also wouldn't back up when put in reverse). in addition to these new problems the rear wheels lock up after a few feet or wheel revolutions. anyone got any ideas as to whats causing these problems or possible things to start looking at. also i observed when he shifted thru the gears the mechanical shift linkage was operable but it was like the tranny wasn't responding to what gear it was in

Does it have fluid? That would cause it not wanting to shift. As far as locking up, not sure, doesnt sound good though.

did a fluid change a week ago, still had same problem