Hey guys, not sure if this is the right forum for this but I'm wondering if anyone could help me out with some insight/advice.

I have an Ibanez RG7321 that is mostly a great guitar, except it has recently developed horrible intonation issues.
The high E and B strings, when in tune, are horribly flat...from the 12th on it's more than a half step off. The B is basically the same, the G is better but bad.
The D and A strings are mostly ok.
The low E and B strings fret slightly sharp as well, but it's not as awful as the high strings.

I've adjusted the intonation on the high strings; both saddles are as far as they'll go towards the nut without popping off the screw and the strings still fret flat. I've adjusted the saddle height as well, no luck there. The neck screws are tight, adjusting the truss rod does nothing...I don't know what else to do from here.
I'm really hoping there isn't a fatal flaw with the guitar itself, but I don't know what else to try.
It is an old set of strings, so I am of course going to change the strings and see if the issue continues, but I doubt that old strings could effect the intonation that much.

Change your strings first, then see the result.
AS the 7321 has no floyd rose, and as it sounded ok before, there are no reason to change.
Is your guitar stored near a heater?