If you added nothing by way of aftermarket parts, I am surprised that you gained anything at all. You need something like a CAT-Back, Intake, drop-ins/hard pipes, or some combination of those to get gains from the tune. The throttle map can be tweaked and you can add features like VDC off from the start or map switching to add Valet or Security Mode(s). If I were you, I would contact UPREV and see if they have something that you are interested in before you go back to your local tuner.
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 2007 350Z NISMO #0618: Zerolift | UPREV | F.I. | Greddy | Competition Clutch | Injector Dynamics | Aeromotive | Pioneer | JL
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