273 not pulling past 4000

I just had my 273 rebuilt, .030 bore. Put it back in and runs great at low rpm around town. But once I hit 4000, it's almost like the engine just stops pulling. And, if you rev up the engine in neutral to around 4000, it starts missing once it idles back down and sputters a bit. Any thoughts? Looking for good places to start checking. Thanks guys.