I also have an Saitek X52 Pro. Something I have noticed is that after an "extended" play sessions, say if I am in a mission for over an hour or so, the aircraft will start to ascend or descend, sharply, often seemingly at random. At first I though I thought it was something I was doing wrong during the mission and the game was simulating some damage to the plane, for example: going into a steep dive, which maybe was "damaging" the plane's elevator in some way. Trimming would have no effect on these massive spikes I was experiencing on the vertical axis.
Honestly, even though I'm sad to admit it, the X52 is overpriced for what it is: a very shoddily built HOTAS with poor quality control. I get that flight-sims enthusiasts are a niche demographic, but seriously... I spent over $200 Canadian for this controller, the stick does not move linearly; often, due to friction it sticks and unsticks, making banking and maneuvering jumpy and the mini-stick drifts all over the place. The whole system consistently causes my computer to blue-screen when I plug or unplug the USB cable.
But at the end of the day, what recourse do I really have? Spend another $400 more on the Warthog? Sigh....