I agree that tyre pressures are unlikely to be the cause if wear is even. Contributing factors could be...
Harder suspension will wear tyres more quickly - be it higher spring rates, higher preload, or higher compression damping (although I've no idea which of these are adjustable on a Supra).
Rubbing between the tyre and wheel arch if suspension is lowered.
A bad batch of tyres, or tyre components, be it carcass, rubber, or whatever.
Personally, I think the truth is that you're just giving it the berries!
