I recently aquired a Reverend Rumblefish P/J...love the bass

But I have a setup issue I need some advise with.
The neck is straight as an arrow, no bow to it at all. It's strung with Fender 9050 flats.
The saddles are *super high*, and in fact on the center two strings, the adjust screws have been replaced with ones that are a little longer...
But, the action is still super low, enough so that it's a little buzzy on the frets in the higher register. Last night I tired to lossen the trussrod to add a little more curve to the neck, thus effectively raising the action a tad. The adjust nut is in fact about all the way loose...How can I get a little more curve into my neck gents?