[mustangII460]

Check your modulator valve at the right/rear corner of the tranny. A vacum line runs to it.

The line could be broke/rotten or the valve could be bad itself. Alot of times fluid will suck up into the the intake from the valve when its bad.

If you take it off, dont lose the little metal rod, inch or so inside when you unbolt it.

The nipple that the vacum hose plugs onto also is a screw. You can turn it 1/4 turn to adjust shift points.