Well, if it's lambda equipped (UDSM, CDM, JDM and most of the rest of the world market) then the ECU will pull enough fuel for close to normal operation in all cases except for throttle positions above 70%... or have you pulled the O2 (Lambda) sensor? What other mods are you running and have you actually tested the AFM (new, doesn't mean it's not broken, is it actually new)?
Other possibilities are excessive knock, a restriction in the exhaust (see: clogged cat), improper ignition timing, improper spark plug gap, bad igniter or coil, water or oil in the plug galley around the plug wire boots.
Check these and post back with your findings.
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