73 deville auto only shifts when I jiggle shifter form N to D

Just put on carb and it shifted for about a hour. So I checked the trans vac line found no leaks, pinches or clogs and still have good pressure from carb to line. Replaced Trans modulator, filter and fluid. Still nothing. It will shift into 2nd when rocking the shifter between N & D and shifts into 3rd when rocking the shifter between 2 & D A Couple people have said its a air bubble but could one get in there without opening the trans? Any help would be greatly appreciated. Or I'll have to take it somewhere before I go crazy.:screwy:

Yup

Sounds like the shift linkage is loose/worn and you are not in the selected gear you think it is, look for worn bushings or a misadjsutment in the linkage. Forget the air bubble, no such thing.

I'll get out there tomorrow and check it. Thanks for the reply