When I have to cut a long board on my table saw, I’ve had difficulty in the past pushing it through the cut without it twisting a couple of degrees one way or the other as it travels. It doesn’t matter if I’m using a miter gauge or my sled. This usually happens when I’m feeding a large piece through and I push either on the sled or the miter gauge, and that’s the problem. The trick is to push on the piece of wood itself not on the miter gauge. Another really big help is to wax your table saw top with car wax. That helps a lot and it also prevents rust.