Based on your response, there are quite a few things you can try before investing $110 on a Torsen diff.
There is a nice website explaining RC vehicle handling.
In the Suspension section, pages 1 & 8 should provide you some good info. But all is good reading if your willing to learn.
Based on your statement of 'not aggressive enough', I'm thinking you mean you don't have enough steering (doesn't turn tightly in corners)
Here's a couple of clips out of it.
Suspension section; page1
In general, you could say that stiffer springs yield less grip on that end of the car, and conversely, softer springs yield more grip.
less grip = less traction = less steering
Suspension section; page 8
For instance: if the front shocks are close to vertical, and the rears are somewhat laid down, the car will have a lot of turn-in steering; it will be very responsive. If the rears are close to vertical ,and the fronts are more laid down, t he car won't have a lot of turn-in, but it will have more steering in the middle of the turn; it will 'square'. In some cases, the rear might actually begin to slide. It works much in the same way as having stiff springs or heavy damping: if you have stiff springs, or heavy damping up front, the initial reaction when you enter a turn will be very strong. In the middle part of the corner the car will probably understeer, but it's the initial reaction that gives the car a 'responsive' character.
Doesn't answer you diff question, but trying to help.......