my daewoo looses power up hills

Hi I have a nubira daewoo(automatic) and every time I go up a hill or even sometimes when I go past 80km my car seems to lose power and once I stop I dies completely and I have to wait around 2minutes then I can start it up again and it goes fine for a little while so I was just wondering if you had any idea on what could be causing this as it is very frustrating trying to avoid hills all the time