intonation very sharp and can't a


I have a gretsh electromatic solidbody made in the late 80's.  I have adjusted the truss rod, put a new bone nut on, but when i tried to intonate, the 12 fret pressed down was sharp about 50% to the next note on all six strings compared with thwe open note.  I moved the saddles all the way back with no improvement.  The guitar has a 24 1/2 scale and has not been modified and is a hardtale.  Can someone point me in the direction to fix this problem?  55 guitarman
How high is the action at the 12th fret? 

When you fret at the 12th, you are actually between 11 and 12 correct?

If action is low and you are checking intonation correctly, your bridge is in the wrong spot.  But before you start carving things up, get someone else to confirm that it's outta whack
just for giggles.... do this

capo fret 1, but not "too tight" as to bend the strings.  Just to make them fret at fret 1.

Now do the 12th fret test at fret 13 instead of 12.    If its fixed, you goobered the nut install.