Don't miss too much on 307 slopes

Hi aleykum friends. I bought a peugeot 307 a week ago. I used the car for half an hour today. It was very nice to switch gears and it didn't skid backwards on the slope. Then on a small steep slope, it skipped back as if the gear was in neutral. I tried it on a slope, likewise, it slips back as if it is idle, it does not eat gas and throws itself forward from the bottom. After 5 minutes, it does not slide back as before. It does not know when to do it, it works, it does not work. I wonder what the reason is, if experienced friends can help me, I would be very happy.

have the oil level checked. In general, this problem can be caused by the solenoid valves.