Frozen Lake Driver
+1 Your battery was dead, so the alternator started charging with a high current to get the battery back up to where it should be, hence increasing load on the engine to make up for the friction in the alternator.Did the battery die when the alternator went out? If so, a low battery would cause your hesitation. And with the time between the swap and now would have given it time to charge.
If your battery is dead and you install a new alternator and jump start the car your the odds of killing the alternator or pretty high. Pull the battery and put it on a charger for the evening (or just pull the negative terminal and put the charger on). If your alternator kicks the bucket in a month, This is why.