I have a 1967 firebird with a 400 engine and trans. Just rebuilt the trans. and have it back in the car.. Will not shift out of first gear..What is problem Help Please!1

Um, rebuilt wrong, or didn't add trans fluid?

(there could be a hundred things hooked up wrong internally or externally)

We may need more to go on for this one. Have you checked all the connections?

The trans is full of fluid first thing i check, How about the vacuum line from the module on the trans. does it hook up to the back of the carb. or the distributor..

Do you have a vacum hose to the modulator valve on the passenger side of the tranny??

Vacuum line is just manifold vacuum

I do not see a totally complete answer above so...

Yes, your tranny will not shift out of 1st gear without that vacuum line to the module on the side of the tranny connected and providing "full" engine vacuum. Full vacuum which can either be from an intake manifold port of a full vacuum port on the carb.

I suggest a vacuum gauge so you can test the various ports. I also recommend a brand new section of vacuum hose because if there are any leaks in it...

I made the mistake of connecting to a carb port that did not have full vacuum (incorrect base plate gasket) and my tranny did not shift until I tested for full vacuum and switched port connections.

If you have a t400 electric kick-down switch at the carb, check to see if shorted...pull the wire off and retry...mine just went bad...maddening!!!