Problem TCC maybe???

I got a problem with my Grand Prix and I think it might be the TCC(Torque onverter Clutch) I'm a try to be as descriptive as possible and hopefully somebody on here can help me....
After I drive on the freeway and I go back to regular street driving the car shifts hard...I don't really know how to explain it but it feels like when in a manual transmission you shift without pressing the clutch all the way down or when you let go of the clutch too fast. I don't think its the transmission because I can street drive all day and won't have that problem, IT ONLY happens after I ran it at high speeds. If I turn the car off and then turn it back on the problem goes aways and it shifts really smooth, in fact you can barely feel the shifts so I don't think its the transmission.
It's a 99 Grand Prix GT 3.8
It has 98k miles on it, the engine is still in great condition and runs excellent. The problem started a couple weeks ago and its only done it a couple of time, the past week it has happened more often. Any help will be greatly appreciated.

The best thing to do is get it scanned with a trans capable scanner. A scanner capable of detecting tranny type DTC error codes. TCC and line pressure/pressure control may not give a SES light but are stored for retrieval. The harsh shifting is probably due to low or high line pressure in which these errors will command. It sounds more tranny related to me.