I have an 84 dodge w150 with a 318. the trans was working but the other day it would only go in to forward gear. In park it tried to move forward, reverse it wouldnt move at all, neutral it moved forward and d,2,1 all moved it forward. The linkage all seems to be moving fine. Fluid is low and needs changed but could this be the problem?  Any help??  Thanks.  

change your fluid and filter first it`s cheap and if that doesn`t work you probably need another trans.  

change fluid and filter while you have the pan off look for broken pieces of parts sound like to me the bands are way out of adjustment. talk to the local trans shop and see what they think.