bspofford,
I had the same thing happen to me, but now I know more about the Q5. It requires a higher front voltage to drive it properly so what you're seeing the dimmer light resulting from less current. If you have a multi-meter, you can measure this yourself and see what I'm talking about. The solution, specifically for the Eastward YJ "U2 Style" light, is the get into the driver and short out the resistor at "R1". That will bring up the current from around 400mA to around 700 mA. You will probably to very happy with this mode. However, if not, then go to the next level and direct drive the Q5 by moving "LED -" to "J1". This will result in around 950mA and you're bound to be happy with that brightness. Let us know how it goes.