When I find the cuts don't line up top to bottom, I have been pushing sideways on the work piece so the blade bends sideways. Increasing the tension reduces the bending but doesn't eliminate it, especially for thick wood.
Toneman is correct, let the blade do the cutting. Every so often, I ease up on cutting and almost let go of the work piece. If the piece moves sideways, I'm pushing sideways.
Hope this gives you some ideas.
Jim