He can’t get square cuts despite repeated realignment of the blade and fence with a dial indicator. He has also realigned the motor and changed out the blade.
The thing about a table saw is that there really aren't that many ways that it can go wrong. If the blade is 90° to the table when the tilt adjustment is set to 0°, and if the rip fence is straight and parallel to the blade, it should be able to make straight rip cuts with square edges. (A rip cut is when you're cutting along the length of a board, with one edge of the board riding along the rip fence.) If the cuts aren't coming out straight when you're fairly certain that the saw is set up correctly, then the problem might not be the saw.
It's pretty strange that your cuts are coming out narrower in the middle than at the ends. The two most likely reasons for this that I can think of are:
warped stock: If you're going to make a straight rip cut, the board you're cutting should have at least one edge that's good and straight. That straight edge has to go up against the fence. If the board is crooked, so that one edge is concave and other convex, or if it otherwise doesn't have a straight edge, then you're not going to get a straight cut. Materials like plywood and MDF are very stable, so those are good choices for testing your saw.
operator error: It's important to keep that straight edge against the fence through the entire cut. Using a featherboard as you described in a comment should help a lot here. Keep an eye on the back end of the rip fence as the cut proceeds and make sure that the board remains tight against the fence there (but don't use a featherboard there, of course). Pushing the board all the way past the blade rather then stopping when the end passes the leading edge may help; if it does, then the blade isn't quite parallel to the fence, and one or the other should be adjusted.
