If the ceilings are high, cover the skylights with an insulated reflective material to reduce the heatload.

The warm air near the ceiling can act as an insulation between the hot roof temperatures. A Lesser temp difference reduces the rate of heat transfer.

If the ceiling to roof area is well insulated, then higher Air Returns will help better heatload the evaporator coil.

Before doing anything expensive, you need to confer with an expert on that particular situation.
udarrell _ 2007

Here is a link that might be useful: udarrell.com