96 plymouth voyager se

I have a 96 plymouth voyager se 3.3 6cyl engine will not shift properly it goes in reverse fine put it in drive it changes first time but when its time for the next shift motor revs up husband changed fluid/ filter put in right fluid road test still not shifting took to tranny shop said i need new tranny my ground wire is coroded near top and looks like some wires near the bottom around tranny may be burnt not sure whats or next place to look this is our family car we need it fixed can not afford rebuilt tranny my husband is only one working:)