You really need to work on your drive train and you should cut and rebrush before the heats and before the final for optimum motor performance, particularly with stock, they take a lot of looking after to keep them at thier best. Also if your drive train is not free your motor will be pulling extra amps this is bad in every way, obviously you will be slower as the motor is not able to rev out as much. But also you will have extra com wear which will mean you will need to recut MORE often.
3600 - 3700 is only ok, not great if you are equalising (you didn't say). I'd be looking for minimum 4000 in for a pretty good set of batteries.
Sort out your drive train first, if it's a belt car it should freewheel for 5-10 seconds, for a shaft driven car I've heard of freewheeling for 30 seconds.