2006 Legacy made loud noise and now barely moves, and rolls in park, but it does move.

The probability of BOTH axles being improperly secured and popping out simultaneously is low, especially if accompanied by movement while in "park". I fear the transmission is damaged, and should be replaced (do NOT try to "rebuild"). Nonetheless, investigate systematically by assuring that the half- shafts are secure, harnesses are clean and tight, etc. Good luck. Draining and checking the ATF for metallic detritus is a no-cost bit of sleuthing too. Usually a loss of throttle is a simple disconnection or failed MAF sensor, but there are more ingredients in this messy stew....