Ok, there are a few things you can do.
Firstly, you can change your diff gears to higher ones. XR6 used 3.23 or 3.45. This however will make the car rev higher on the freeway.
Secondy, you can do some engine mods which involve performance cam shafts etc. Check out www.crowcams.com.au.
Finally, if you want some real GO out of your EA off the line, put a 5 speed in the thing. IT's the best mod I have ever done, and I guarentee everyone else who has done it would agree.