I have a 4r55e trans that will only go into reverse and in D2, what could be wrong?

Is the OD light flashing on and off? More than likely the problem is the solenoid pack in side the trans. Usually these trans get to much pressure due to a malfunction solenoid that controls the pressure. When that happens the trans goes into FMEM, failure management effect mode. Another cause could be the throttle position switch on the engine, but not likely. If the problem is too much pressure in the trans get it fixed now because it will blow the front seal out and you will have trans fluid all over the place, and if you dont stop in time it will burn up the trans.