Ford Repair: 84 mustang c4, vacuum line, carbuerator

Question
I just replaced the tranny in my 84 mustang (3.8) and its not shifting into second when it should or third at all.  The fluid level is good. Could it be the modulator, or maybe the vacuum line? Any suggestions would help. Thanks.
Charlie

Answer
it is probably the vacuume line.  Hook the hose directly to the back of the carbuerator or a fitting on the intake manifold.  If that doesnt help the problem it may just need a rebuild.  My experience with c4 transmissions is that the bands tend to wear out quickly, and they are notorious for having poor second to third shifts.