Need help for 67 Firebird with tranny problem

Hi -- Newb here but I love my Firebird and could use advice on a problem -- for about two weeks my bird was real slow shifting into reverse when the car was cold (it's an automatic transmission) -- just this weekend it wouldn't shift into drive (any of them) or reverse...just sits there growling without going into gear. If you have ideas on the problem or how to fix it, I'd appreciate it, thanks.

sounds like a stopped up transmission filter dude. have it flushed and a new filter put in and that should do it. if not you may have clutch problems and will need to be rebuilt.