I've found 3 AAAs to be a bit anemic on low-impedance loads. I would not be surprised if the voltage sags when running them around 3C like that. I'd try 2.2 ohms or above. It varies with the batteries, though.
AA batteries would probably be a better choice for a 3 cell mod. I prefer 4 cells when using AAAs, using 3 ohm coils. It depends upon what you are used to, I guess.