Megane 2.0 ALIZE 1998, Transmission problems

Hi, . The problem is when i stop the car it feels like the auto-transmission is still in 2nd gear, rpm is around 1100-1200 and when it shifts down it comes with a thump (i have to be careful not to be too close to the next car). In some instances i can select the 1 st.gear and the car will not move, and the rpm is up, if i throttle a little then it will kick in gear. This problem with the transmission seems to be worse if the car has warmed up. I have shifted the car down manualy (from D - 2 - 1 ) and the problem is not there.

Any suggestions ? Oli.

p.s. Oil and filter have been changed.