Right I reckon you're under geared.
http://www.racing-cars.com/images/Te...sx_page_36.jpg
According to this, and given that the standard idles are 23/33, even if you've got an 83T spur (couldn't find what size the spur gear is), you're running 9.32 internal ratio.
With 5.5T motors we're running around 9.5, so you see you're running a ratio for a much more powerful and revving motor.
For the 2WD, is it a 7.5T as well ? If so that's about right I reckon.