Maybe I missed this but scanning through it seems like this has been made incredibly complicated when it is fairly easy.
lift = 1/2 (p v2 A Cl) where p = air density. As air density goes down for the given altitude total lift possible will go down. CL is limited by AOA. Lift has to remain equal to weight so put the aircraft at say 50 knots (assume it is at stall) at critical AOA with lift and weight both equaling 3000 pounds.
Now take this aircraft and increase its altitude which lowers its total lift, lets say 2800 just to give it a number. Now we are already at critical AOA, the area of the wing can't change, and this leaves only speed left. We must increase our speed in this situation to regain 3000 pounds of lift to equal weight.
I have never read this airflow separation from thinner air before till it was posted here. This obviously doesn't mean it's not true, but I would love to know more if someone can break it down barney style for me. Thanks.