I can't seem to figure any other solution. I bought a used bass and it seems it has a problem. My saddles are down as far as they can go. My trust rod has been tightened to the point that the strings are buzzing on the upper frets, and still the action is way too high on the lower part of the strings. It would seem that something needs to lift the middle of the bass. Are shims the only answer? Has anyone done this? Am I missing something basic?