This might be a dumb suggestion but have you checked your table saw arbor and arbor bearings. To me it sounds like there is too much load on this motor if it runs fine outside of the table saw. I know nothing about this saw therefore don't know the configuration of how the arbor is tied to the motor. On a typical saw, with your belt removed you should be able to spin your arbor completely free and should have zero hard spots with no play.

I've recently replaced my arbor bearings on my saw and seeing how the saw runs now I should have done this years ago.