Im a newbie, so please tolerate my ignorance as i describe my issue.

I have a 69 Camaro SS with a 350 engine and an automatic turbo 350 transmission.

I was having issues shifting from 1st to 2nd gear automatically...I can shift maunally from 1 to 2 to 3rd without issues.

In drive, it has an issue going from 1st to 2nd - it will rev very very high before shifting.

I thought i had a transmission issue so i brought it to a local tranny shop - they told me to replace the vacuum modulator and also check the hose going from the T in the manifold to the modulator for obstructions and that i would most likely find my issue.

Needless to say, i replaced the modulator and checked the hose but still have the issue.

What else should i be checking?  

Is the vaccum source (manifold vaccum)? If not, it wont shift properly. Also, is the vaccum source totaly committed to just the modulator. If not, hook it up so the modulator has it's own vaccum source.  

The vacuum source is the manifold - but it shares it with the power brakes - has a T off of the manifold.  

Hook it up independently and see what happens.  

Need more info if not solved, Is the vacuum modulator adjustable? What happened prior to the transmission acting up? (what where you doing or what changed it from normal)