I'm trying to adjust a Fender American Jazz with a low action. I keep getting string buzz that actually make the 18th and 19th fretted notes sound the same on both the A and D strings. I raised the saddles on those two strings but now the action weird because the E and G strings action is low. I first thought it was a high fret since the 20th fret sounds but before I missed with the truss and bridge the action was lower. Help. Any suggestions. Thanks.