My '05 does the exact same thing, on mine I've diagnosed it to be a faulty or gunked up pressure control solenoid in my transmission.
Pretty difficult job to replace it from what I can see and have heard, either drop the tranny or do a whole lot of other half drops to call it that, in order to reach the panel to replace the cheap as **** sensor.
Ever hear of seafoam? They make a transmission cleaning fluid in addition to their normal injector cleaner, probably going to do that and put in a shift kit in a few weeks as either solution has worked well for most people, why not combine them?
But really, like kind of "uneasy" acceleration, and shifts a bit higher in the rpm's? Try just changing out your tranny fluid and filter, when I did mine it was DISGUSTING! Obviously no one had ever done it before (I got my 05 GT at 59,000) and because of that my sensor is now gunked up and gives me problems once in a while. Turning the car off and back on solves it until it randomly occurs again.
Edit: And if it IS your transmission's PCS, it DOES throw a code, until you restart the car, so unless you have it scanned while it's acting up, you won't find any codes relating to that.
