mid rpm flat spot

car is a 91 5.0. it was not idling at all so i replaced the ignition module. it idles and runs very well now... until about 3800 rpm. with and without load it falls flat on its face (sounds like a soft touch rev limiter almost) at between 3500 and 4000 rpm. since it happens without load as well as loaded i am assuming it is ignition related. i'm leaning toward a bad distributor. what do you guys think?
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I had an ignition module on one of my gt's that was partially faulty and caused it to cut-out between 3500 and 4500 rpm but ran great before 3500 and after 4500,but you said you already changed the module,but there is always the chance of a new part bein bad.you could have it checked for free at autozone just to make sure its good eventhough its new.the pip inside the distributer could be bad but i wouldnt replace the whole dist.i would just buy the pip from autozone and install it yourself.its only $24 bucks which is alot cheaper than a $100 dollar dist.unless your factory rev limiter has gone back inside of your computer.it cuts out at 6250 rpm.