2004 Mazda 6 Engine Flutter

I apologize, I may not know the correct engine terminology...But at around 2800 to 3200 RPM's (approx. 68-72 MPH) when I let off the gas slightly my engine will "flutter". Almost like the fuel is getting cut off too quickly. I have only noticed it at high speeds. Sparkplugs are less that a year old. A new Crankshaft Positioning Sensor (I think that was name of it? Its right on top of the engine) was changed in September 2014. That actually seemed to help for a short time. It has never made my car stall, but Im afraid the problem might get worse. What could be causing this??

Thank you for the help.