Do a search on these boards for the stick by manufactors name (I don't know who makes an (X52) and scaling. A number of people have posted their set-ups with that stick, that may help.
On the other hand, unless your very heavy handed with your stick the default slider setting should be a good starting point. Scaling is mostly fine tuning to your style of flying.
As to whether your "stalling" or "compressing", the best way is to check what speed your running is to bring up the clipboard, and click on E6B. This will give you your alt, speed, range and so on. Most planes "cruise" between 280-400 mph. Check to see if thats where you are. If not, your throttle may be out of wack. If you are then like Lusche said, you maybe compressing.
Best thing to do is to spend some time in the training arena and get with one of the trainers. They can help you get your stick squared away while your working on it, in stead of checking here then going to try some stuff then come back with results. Theres enough stuff to learn with out having to fight with your stick!
oh, and welcome to Aces High!