Air decreasing pressure above the wing has nothing to do with the speed of the air, it is actually due to inertia. Air always wants to fill empty spaces due to the fact that there is something called static air pressure. All air molecules want to push equally in all directions so when there is a space without air, the molecules fill the space due to there being no air molecules in the space to push against them. This is what happens with a wing, the molecules want to fill the space above the wing but they have trouble doing that due to their inertia.
Think about a car turning, you can't just go 100 mph and turn the in the same radius that you do when your going 10 mph. The same principle applies to the air molecules. They have a hard time filling the space and therefore the space has less air molecules then the atmospheric pressure. The less molecules on top means less static pressure on the top then on the bottom where the air is at atmospheric pressure. This forces the wing up due to the difference in force, so basically what lifts a wing up is suction.
If you want to say that air has a further distance to travel over the top and therefore goes faster, there is a simple way to prove that wrong. A completely flat surface can create lift as long as you tilt it relative to the airflow. The air has to travel the same length over the top and the bottom yet it still creates lift.
For stalls I'm not sure but I have a theory that in a stall, there's turbulent flow due to the air from the bottom trying to reach the top and vice versa but this only occurs behind the wing surface. Over the wing surface the air completely stops moving and just stays attached to the wing and therefore reaches atmospheric pressure.
This would explain how in a stall a wing both produces more drag and less lift because the equalization of pressures on both surfaces of the wing cancels the lift but there is still low pressure air behind the wing which sucks it back acting as drag.
Think about when your in a car and you open boot and put down the seats. Now the airflow at the back of the car will obviously be stalling but what about where you are sitting? The air feels normal there, it's not moving, it simply sticks with the car. Also when you look at a stalled wing in a wind tunnel with streams of smoke flowing by, you'll notice that there is no smoke streams right above the wing, just where the air is looping behind the wing. This is probably because the air isn't actually moving right above the wing, it's simply staying with the wing.
The stall thing is just a theory of mine but the thing about how inertia creates lift is the correct way that wings produce lift.