Matt,
Sounds like you are starting to lose volume in the pan or you're uncovering the pickup on high acceleration/speed.
Without knowing or assuming anything else about how the engine is assembled, your idea about trying an extra quart of
oil would be something worth trying.
Also, if you're pulling your
oil pressure from the rear of the block, it's not uncommon to see
oil pressures like that, since it's getting "residual" pressure after all the bearings/lifters/etc. have been fed.