1998 Subaru Legacy wont stay running

You mean the engine stalls or it won't shift through the gears as well. Just how many miles on this car?

Sounds like a torque converter issue but diagnose properly before assuming/fixating on one thing. Is the "check engine" light on? If yes - get codes / if no - check ATF fluid level / check for vacuum leak(s) / fuel pressure. Check source: http://www.justanswer.com/subaru/2mn1t-1998-subaru-outback- starts-fine-stalls-when-put-gear.html#re.v/327/ and http://www.cargurus.com/Cars/Discussion-c3487_ds617372 and more, searched for: 1998 subaru legacy stalling gear