If your piece is tack-fired, you will need to select a fire polish schedule very carefully. Have you tried using the same schedule that you used to tack-fire your piece? I would be careful not to go any higher in your process temperature, because you will lose a little of the relief (depth and detail) of your current firing each time you fire, due to accumulated heat history.
You might try using your tack-firing schedule at a lower process temperature, for instance 10 degrees F lower and see if that works.
Be sure to use a VERY conservative annealing cycle, because your piece has been tack-fired. This video might be helpful: https://videos.bullseyeglass.com/videos/fusing-basics/
Good luck! Let us know what happens.