My Renault Scenic over revs in low gear?

I have a 1.6 Scenic automatic transmission. Apart from the mouldy rear seat belts and creaking when under braking, there now seems to be a problem with the gearbox. When driving through town, pulling off or just generally driving slowly, the gears seem to slip, the engine over revs (heavy foot syndrome) until about 3000rpm it seems to find a gear and drive on as normal. I have found this happpening on hill starts also. So, has anyone got any tips or advice for this issue, please?