I also have an R34 GTT with similar or same problem.
My car has full 3inch exhaust and dump pipe, apexi power fc, K&N air filter and is run at standard boost. Note: The extras have just amplified the problem.
1. For some reason, in approximately the first 30 minutes of driving I will get random misfiring? (engine sounding like a WRX). Sometimes it starts like it, then goes and some times it just cuts in whilst driving. It is usually worse during winter and cool weather. Considering most of my trips are less than 30 minutes, it happens a lot and is quite annoying.
When this happens, the smell of fuel (sulfur smell) is stronger.
2. Also when up around the 4500 - 5000rpm mark the car (when warm) just seems to give out, sort of misfiring.
To answer part of your question. I had the same problem "slip light comes on and trac control light and the engine light and abs aswell". Oh and the actual traction control wouldn't work whilst these lights were up. I think I may have caused this problem by travelling too fast around a bumpy corner whilst the traction control was on (but not 100% sure). I noticed that when all of the mentioned lights came on, the car would splutter slightly. The problem of the dash lights coming up was taken away when power fc installed. I think also a good auto electrician may be able to fix the computer error.
Looking at the manual which I purchased after the incident, states that you shouldn't spin the wheels with the traction control on whilst going around a corner.
I am still not sure if my current problem is actually the same problem (without the dash lights coming on), just enhanced by the addons. Although now when the car is misfiring, the traction control still operates correctly.
I have had mechanics check out the coils + tuned etc, they had the car for quite some time and they couldn't seem to find the problem. They said the coils looked fine.
I am not really mechanically minded. I only really know what I have been shown which isn't much.
I have read through all the old posts and wondered if taping the coils etc will correct my car problems or should I find second opinion mechanic and have re-tuned etc.
I love all skylines and can't stand the thought that my car is running shite.
Any help would be greatly appreciated.