I would suspect the batteries....my VIP is slightly brighter using NIMH 2400mah..Some of the high capacity NIMH seem to restrict the current more than low capacity batts, which is what creates the slightly improved brightness in the VIP. it could be that your brand battery is one of the many. I have had good luck using the CTA brand 2400 mah NIMH. The part about the low mod is typical though...to access low you have to click the kroll on and off, when switching from high or medium. I hardly ever use low with rechargable pack though? I mean what is the point? Every now and then it is handy as a reading light in the car at night so as not to blind the driver, but it works perfectly fine for that.
NIMH also have to be cycled a few times to really be charged to their full capacity, you wait a few charges before making any real assumptions.