My carburated 305 loses power around 3k rpm. I have found more than 3 vacuum lines disconnected, so I know that's it. Does anyone have any chart or picture of the vacuum routing for an 84 Firebird 305?

 

I don't have the diagram, unfortunately. However, vacuum leaks rarely have any effect on full throttle/high RPM performance.

They usually cause problems at idle and part throttle drivability.

Sounds more like your carb secondaries aren't opening up, you've got a fuel restriction (maybe jsut a clogged filter) or maybe the EFE valve on the passenger side exhaust manfiold is stuck shut (causing massive back pressure on that bank of cylinders). These are all very common causes for these motors to "lay down" at higher RPMs.

 

Hmm, could it be my timing?