So, when I first start the car for the day and start driving. I make it maybe a half mile and notice it wont shift to the last gear at 55. Then, it will start jittering/sputtering and wont accelerate. The only thing I've found that I can do is put it in Neutral, shut it off, turn it back on, then back into drive. Then it will run almost like normal for the rest of the day. Any guesses as to the cause and potential fixes?

Thanks!