I don't care what NOS says about the stock fuel pump, I would upgrade that first. It can make 47psi at idle, but on a dry kit, the extra fuel is supplied by spiking the fuel presure up to around 80psi at the regulator. That pump is probably falling on it's face under load, and not supplying enough fuel. You run lean and detonate.
While you're at it, install a new fuel filter.
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Moxie Racing
The Nitrous Oxide Information Site