The problem I'm having with them is that they run very flat with no punch at all
I don't think you need to "break in" batteries. They have allready been cycled by the matchers. Wouldn't that do the trick?
GP3300 do get better after a few runs.
I think you need to discharge like this. Run the race, discharge at 30 till cut-off. Put away.
Before you charge, put them in your tray at like .5 (volts) setting till its done, then charge right away. Sounds like you are not traying the cells RIGHT BEFORE you charge. Thats critical.