Good morning everyone. New to the forum and new to Y blocks, Fordomatics and 55 Tbird. My little car appears to be 95% original and since it's that way I would like to maintain everything I possibly can. However, the transmission doesn't seem to go into high (if I have the correct understanding of the basic transmission function). I can select Lo or Dr, the car shifts between them fine manually. What I don't feel is a shift from intermediate (which is where I think the car starts out while Dr is selected) to Hi. Is this a possible problem with bands, servo, or something else entirely? Are these transmissions reliable after a rebuild, or should I just go with C4? I have some engine questions too. I think I'll make a different post for them. 
Thank you in advance for any help.
JH