A few things. The fans coming on with AC uses a differnt set of relays to turn them on. You could have a bad fan relay, bad tempature sensor or a problem in the wiring for the sensor.
Since the fans come on with the AC, that rules out a bad fan motor. So start backing up through the system. Recommend not running the motor hot to the red line or you'll harm that new motor.
If you had a shop install the motor, take it back.
Nice to hear someone like's their Aztec enough to remotor. The later production ones without the clading look sharp. But, as in recent history with the Fairo, Bonnievile and the Aztec and now the departed GTO, Pontiac gets it right when the plug gets pulled.
Good luck, post back when you get this fixed.