I have a JP-90 that sounds great, unless you slap it. Then the E and G strings sound fine, and the A and D sound dull and lifeless. The A isn't too bad unless you slap it open, and then you get a dull "thwumm" sort of sound. I've tried two bridges, and I reglued the nut (it was loose) but it didn't help. The nut is fitted pretty well, the strings aren't slopping around in it, and I filed the top down to where it should be, because I really thought this was a nut problem. Now I really don't know what it could be. If you pop the G, it sounds bright and snappy, but the D sounds like a flatwound. It had Danelectro nickel roundwounds on it, and I thought they might be dying, so I put a new set of Picato nickels on it, and it sounds exactly the same. Tried a different pickup. No dice. This bass sounds good fingerstyle. All the strings sound bright and lively. It seems like it should slap OK, and I think it did when I first got it, but now I'm not sure. It seems like something must be loose, but what? I'm lost.