Had a similar issue with a stumble always at the same load point. Was caused by the delay between switching fuel voltage. Bypass the resistor as per above post. You can find the instructions on stealth316 in the fuelpump hotline page.
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1990 JDM GTO TT, oohnoo fuel loop & rail adapters, K&N FIPK, Vi-PEC plug-in V44 EMS, Iridium plugs, Turbo XS racing BOV, ARC SMIC's
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