Help needed with my 355

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hello all, got a problem i cant seem to solve and i need any and everyones advice. i bought a 84 chevy hot rod with a 355 (465hp at the wheels). problem is when the engine is under load (at about 2500- 3000 rpms) i start getting bad hesitation and some backfiriing. i have a holley 750 dual pumper carb and had it thourghly checked out, but that wasnt the problem. changed my plugs (ac delco v63c racing plugs) and still no improvement. she pulls strong until that 3000 rpm range then she feels like she`s bogging down. what do you guys suggest i check next? ignition system mabye? drop me a line it will be greatly appreciated