So was out cruising last night in my 63 convert, my cruise o matic seems to shift through the three speeds very smoothly at low speeds. Once on the highway I fine I'm having to almost drive like a manual transmission. Letting up on the gas just slightly to get it to shift from 1st to 2nd and having to do the same to shift from 2nd to 3rd. Once in third gear I fine it very sensitive to the gas down shifting very easily with just the slightest acceleration. Any ideas of what could be the problem. I have read on here about adjusting vacuum modulator, do you think this would help?