Apparently you can get different results by calling the TOKSIM_Advance function more than once per loop, so try lowering the step value from 1.5 to 0.75 (or possibly 1.0) and calling the function twice -
TOKSIM_Advance( 0.75 / FPS , 2.0 )
TOKSIM_Advance( 0.75 / FPS , 2.0 )
TOKSIM_Advance( 0.75 / FPS , 2.0 )
TOKSIM_Advance( 0.75 / FPS , 2.0 )