transmission shifting problems

[R. A. Frost]

We have a 67 Firebird with a t350 transmission. It now will not shift until around 4,500 rpms unless you shift manually. Any ideas what the problem might be? Thank you very much.

 

[melsg5]

Have you tried adjusting the shift cable attached to the carburetor linkage?

 

[Zimgxp]

Sticky Govenor?