Hey man ,sounds like you have nothing to loose w/the old one.Sounds like
maybe a valve body issue. valve body is responsiable for shifting ,and
shifting into gear. Do this!!! Get a can of seafoam auto trans tune($7
advance auto parts). Dump it all in as you say goodby to the trans.Idle the
engine for 45 minutes ,shifting it occasionally.If you got any hope at all,
this is it! Sea foam is  the ticket to clean out crud and loosen up a long
dormant auto trans.Good Luck