I'm no expert, but I'd guess that maybe your throttle cable is sticking.
I think there was a TSB or recall for some model years.
Hopefully someone more mechanically savvy can shed some light on this.
Otherwise, I get a little of this as well on occasion - lift off the throttle in gear, and instead of the revs dropping right away, the car will linger, maybe even pick up a little bit more speed before the revs drops.
Pretty sure that it's just good old Duratec throttle hang.
Good luck!
