Peugout 206 gearbox fault?

Please help when i start my 206 auto it will not go forward if there is a slight incline, it justs revs as if in neutral then eventually at v high revs it starts to creep forward slowly. It behaves fine once its running at full temp. Howver unitl it gets to full temp it will sometimes stick in gear all of a sudden with a bit of a jolt especially on hills, and you have to turn it off and re-start the engine in order to get it to change gear. Someone mentioned it might be the engine managment unit?