I have a 95 chevy tahoe we put in a rebuilt transmission well when we are going anywhere we have to manually change the gears because it will not by it self and it has no power what could it be? We heard that the computer is not recognizing it and it will have to be program to it could that be our problem?

 

Ideally the transmission adapts should be reset for best performance, but it wouldn't cause it to not shift at all or slip.
It sounds like the transmission was either not rebuilt or not installed correctly. Hope you got a guarantee on the parts & labour.