How much are you willing to do yourself? There are a few things you can try that might help your problem.
By the sounds of your other thread though the car is running hugely rich, which would explain the problems you're having, so I'd be checking things that will alter the amount of fuel being pumped in. I'm definitely not a mechanic but check these things in no particular order:
1) Clean the AFM with electrical contact cleaner
2) Change the fuel filter
3) Check the output from the throttle position sensor, you can of course do this with the ignition on and the motor off, so you don't have to rev the crap out of it. You're basically after a smooth linear voltage increase. I think the standard range is 0.65V (closed throttle) through to 4.8V (full throttle), but look it up because I'm going from memory and am probably wrong lol
4) It shouldn't make a difference but swap to another known good fuel pump
5) Swap ECUs with someone else, keeping in mind that S1 ECUs are different to S2. If you have an ignitor box (bolted to the top of the engine, right up the back near the firewall, behind the stock BOV) then you need a S1 ECU.
I haven't listed things like sticking injectors because you've said the carbon buildup is consistent across all 6 cyls.
Failing this, if you'd still like someone to have a look at it, you could try contacting Dan (send a PM to 3lit3 32 on these forums), he knows his Skylines and has helped out quite a few members of this board. I'm not sure whether he's having time off over the break but it never hurts to check