problem between 3 to 4.5 rpm

when i get on the highway and really push the gas when the car gets between 3 and 4.5 rpms the car sounds as if the cylinders are out of sync and the exhaust sounds like its pulsing. when this happens the car has very little acceleration. i have a aftermarket intake and a exhaust can on it if that might affect it. i have no idea what it could be.

check for leakes, then make sure nothing could be clogged, is this at WOT or just cruising?

only at WOT and check leaks were?