Just got done putting my intake manifold and head cylinder back together. When I rev, it wont go past 3k rpm. I took my spark plugs out and i notice that oil is all over the plugs on 1, 3, and 4 (all three are missing spark plug seals).

But could that be why my car wont rev past 3000 rpm?

 

Fix the seals and recheck your cam and ignition timing.