Report back on the evaporator. It sure sounds like it's frozen.

Efficiency isn't the same thing as power consumption. At 95 degree ambient, the refrigeration cycle is more *efficient*, but it consumes more power. Here's an analogy: a lawn mower engine is very inefficient, but because it's not doing much work, it doesn't consume much fuel. A jet engine is extremely efficient, but because it's developing so much power it consumes a lot of fuel.

On a hot day, the AC runs more *efficiently*, but it also runs more *often*, so it consumes more total power. Efficiency in a refrigeration cycle is measured by the amount of heat transferred to the hot side as a function of the energy put into the cycle.

75 is terrible. You should be able to achieve 68 degrees at 95 degree ambient temperature, even with a high wet bulb (dew point).

One other thing -- if your furnace filter is old and quite dirty, this will reduce airflow across the evaporator which can also lead to a freeze up.