I also remember that on GM'* and most other cars, the A/C will turn on with the defroster to pull moisture out of the air, as it sticks to the A/C evaporator, this helps clear the windshield. It also could be that with air in the cooling system, the temperature sensor was not submerged and therefore not giving a proper reading. "It took forever to heat up"
In regards to it being sluggish on hills. You ARE running premium gas, right? If not use an octane additive. Also, if you haven't done so since buying the car, change the oil in the supercharger for good measure.