Chevynova400

Hi, I just purchased a 2001 GT 4.6l with 60,000 miles on it. It has an automatic transmission. It shifts fine. When driving around 40 mph, when I take my foot off the gas, you can feel it hold back. This is with overdrive on. It does not do it at any other speed. Is this normal? Its like its between gears and goes back to the lower gear. If you take your foot off the gas slowly it does not happen. I appreciate your response. I have had my mustang a few months and it is a great car. Putting new front pads and rotors on this weekend.