I tried in 3 default airplanes with the same negative result, slew option it works fine in all aircrafts.
I'm sorry, but I cannot reproduce the problem, and nobody ever reported it before.
Recently I have had a cooling issue on cpu (95-100 C) which of course is fixed but if I remember correctly the problem started after that.
This explains it very clearly, and definitely proves GSX doesn't have anything to do with this. If you are running your system so hot, it's very likely that even a momentary request for a bit more CPU power, would trigger the CPU self-protection against burning, which might likely crash or freeze your system.
Don't overclock, you surely don't need it while *customizing* an airport.
Customization page opens but it is not clicable.
Again, cannot reproduce it, and nobody reported it before but, of course, if with this you mean it's not clickable *after* the freeze, it's normal that nothing would work correctly, if your hardware froze.