Down Under Dude,
this response is my shotgun approach to diagnosing the problem (very effective against small mammals...er, I mean problems). Hope it helps:
The rear and center diffs would be a good place to start. Since you've been driving it around for 4 months, you know how easy it is to gun the throttle on a soft surface like gravel and break the rear end loose almost immediately. Please don't make us try to believe you've never done this...we all know the truth
. Spectacular 360's yes, but murder on the diff
. Also, you may want to check the clutch shoes since they are nylon/plastic and may have worn considerably and this would also affect power delivery. Lastly, if you drove through some water and let your car sit, it is possible (but not very likely) that your bearings may have seized. I'm sure you've dreaded hearing this but it's tool time...your fun is officially on hold.
Recently I have had some trouble with my brake linkage and have had to make some adjustments. Apparently, the pads were pressing on the discs continually and were scrubbing a lot of speed due to its design. I'm doubtful this would be your problem however, I thought I'd mention it anyway. I am working on a simple design to cause the brakes to return to their neutral position better but I haven't had the time or initiative lately. I'll make a post later about this when I figure something out and it actually works longer than one run down the street.
Please let us know what you find out.