ok ,well it's not a heat issue. Temperatures actually increase for a short period after you have come off throttle. It's not the fulling either, as you say you are in the 11's. It is defo a timing issue, and i would still say it's a knock strategy related issue.

You need to go over the engine loom and make sure everything is spot on. I have seen a lot of knock sensor plugs where bare wire can be seen where it goes into the plug, and they short out against each other. Try unscrewing the knock sensor, and wrapping it with cloth, and then tucking it in the heater box. This sometimes has an effect and cures the problem, but often makes it worse too.

The ecu for some reason becomes very sensitive to knock inputs, and retards the ignition for fun. It may be that you need another ECU - if you can borrow one off a mate local then defo try this.