Hotter air when the compressor is running faster (due to higher engine speed) sounds like an issue with your condenser. If you don't condense the refrigerant vapor it will make it to the evaporator as a hot gas (Industrial refer systems call a similar operation 'hot gassing' and use it to thaw the evaporator coils), lower speeds (and lower refrigerant flow) can likely still condense quick enough, but increase the flow and it can't remove the heat fast enough and the heat will leave at your evaporator instead. Are your fans still kicking on when the A/C button is illuminated? Is there something obstructing air flow over the condenser?