Did you use a 2 watt resistor.. mine get hot (but not as hot as the heat syncs for the LEDs.. I checked it out with a temperature gun and it stabilized out at a constant temperature.
if you increase the size of the resistor, you will get less current and hence less power (and dimmer LEDs).. maybe your LEDs don't quite have the same forward voltage? if they are dropping less than 3.2v each then there will be more voltage (and power) going through the resistor.
check out this guys instructable on driving LEDs http://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/
you could use one of those circuits instead of just a resistor.
I have actually made a new version of the lamp that uses transistors and an Arduino to control the LEDs'.. the idea behind this is it has a sleep timer.. I need to post that .. but the base is a larger base