I see, I only ask the specific because the 6 speed has a common TCM problem where the fluid pressure switches break and then your shifts aren't very smooth. It seems like you have slip the way you explain, I remember reading that the 4 and 6 both have problems with the solenoid actuator, that was common as well. Go get your OBDII scanned; scan the transmission exactly and see if you have a P0989 Fluid Pressure Sensor/Switch Circuit Low code, you can do that for free at Autozone or where ever you please. If you have that code on this 6 speed then I must persist you have a blown TCM fluid pressure switch. If you see metallic flakes on your trans dipstick, I can't help you from there it's either both the TCM and worn wave plates or some other problem.
New TCM is relatively $500 for the part but the actual repair of the switches is a 15 dollar kit and you can basically do it yourself. Also check your transmission fluid via dipstick when the engine is warmed after 20 minutes of driving, and look at the color, the level, shine the fluid in a light source to see if any flakes are present. If it doesn't look all that well, get it flushed including the torque converter and refilled with Dexron VI and see if your shifting improves. You don't have much to lose anyhow by draining the fluid for new, a failing transmission is already in your hands. If it does improve for the first 500 miles, and make sure you take it easy during that time, then I persist it is the fluid pressure switches. If not, if your drive is jumping more than a kid in a bounce house then I would suspect slippage. The shifts won't immediately fixed, it''l come back after 400 or 500 miles being changed but they will be smoother so keep that in mind. Also, how many miles are on the car? 60-90,000 miles I presume?
Video is what to look for, below is the 989 code, and a simple guide to the color of trans fluid in case you or anyone else doesn't watch the video.
Sorry for a big post but this is important to know.