[BrianG]

What voltage did it start at? It's possible you might have overdischarged it a little. It could also be getting old (you didn't define how long "a while back" is).

Also, did you balance at the same time? If so, the balancer does bleed some capacity away while doing its job, but an extra ~600mAh sounds a bit high unless the balancer was on for the majority of the charge.

From the sounds of it, those NiMHs are working too hard or are "optimistically" rated. I usually put right around 3100-3200 mAh back into my GP3300 cells (non-matched or zapped). If NiMHs heat up too much or drain too hard during running, it could reduce their capacity.