What you are experiencing is natural ground movement caused by the hydration and subsequent drying of the ground.....probably heavy in clay. This effectively raises and lowers your house. Even though the frost line in most of Texas is probably fairly shallow (12" to 18"?), that the pads are moving suggests that they are not deep enough.....that is, down far enough so that surface water from rains don't reach them.
there is the possibility that they are deep enough, but during rains, the water collects at the bottom of the posts and pads, saturating the ground...then drying out. If this is the case, the way to fix it is to seal off the tops of the posts going down to the pads below grade. If the pads are setting on the surface, the only fix I can think of is to, one at a time, dig them down to well below the frost line, the tightly compact the soil over the top of it and around the post, to keep water out.