T3 to T2 is an easy, short walk, just follow the signs. It will be quicker than finding the AirTrain.
Like has been said, you will need to collect your checked baggage to clear customs, the recheck them and clear security. I've done it a few times, it's easy enough, although be warned than immigration at JFK is one step away from Hell on Earth. I'll let you decide whether that's one step better or worse...