OJazem; I'm not familiar at all with Skoda, but.... If the Skoda engine uses VVT (variable valve timing) it could very well be the problem. Too heavy of an oil can cause sluggishness because the VVT can't change as needed. A good quality (synthetic, if the manufacturer suggests) 5W30 would be good. Modern cars are designed to run thinner viscosity oils than we are used to. It will also help fuel economy.
Let us know if you still have stalling issues afterwards. There are other possibilities for that.