Running rough

I just got my IROC back from the shippers & she runs rough. It will idle no problem but when you put her into gear & give her some gas she hesitates even when running steady you can feel the lagging.
I'm going to check the timing ? Could it be any of the vacuum lines as well it's a 305// 4 barrel. I put an K&N Air filter package on a few months ago ?
Thx in advance.
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vacuum leak.
-- 98 Camaro

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