Two things occur to me on this:

1. what is the circumfrnace of the tires on there now.......I.E. are you using a taller porifle than say a 60 series.

2. When you say sport cam what kind of cam are we talking about spec wise. If you using something similar to a NISMO option 2 cam AND you're stuck with the stock gearbox the car will drop 3000 RPM's between 2nd and 3rd. That cam will do nothing below 5500 RPM and with what your motor is limited to it like isn't pulling past 7800-8000 range.................so when you shift to 3rd the motor falls off the cam.

If its a cam ground with mid-range in mind then chage your overall gearing so that your in 3rd all the time........your likely loosing time having to shift than you gain with the burst of power in second.

Tom