I killed mine at 228rwkw. I went to the track a lot. Heat kills them so do a couple of things. Be very careful when it's cold - no boosting or highish revs. It takes longer than your engine to warm up too.
Put a transmission fluid temp guage in your car. Cheapest safety device ever. I just used an oil temp guage and plumbed it into the send line to the transmission cooler. Keep an eye on the temps and don't let it go over 100 degrees.
Another thing you can do is a valve body upgrade from MV automatics in Adelaide. About $350 plus fitting. You take yours out and send it away then get it back 2 weeks later and refit. I did it myself in my garage without much knowledge and it was a c**t of a job but it was possible.
The valve body increases the speed of the shifts which decreases the heat created.
You could try putting Redline Racing ATF in. I put the High temp ATF in but a, it was too late for mine at that stage although I didn't know it at the time, and b, I should have put the racing one in. The racing one has no friction modifiers and every other fluid out there does. The friction modifiers create slip to make the shifts comfortable. Slip = heat = death.
Also I don't believe you need to replace the standard R34 auto cooler. If any R33 owners are reading this - you do need to replace it.