Low rpm on 454

Fuel filter on the slow engine would be a good place to start. How recently did both spin up to 4400? It probably wouldn't be a bad idea to look at the props but if you say it was smooth and quiet they're probably alright. I'm assuming they share fuel or at least were both filled up at the same source? When were they tuned up? Does it rev up to 4400 in neutral? Don't really know but those are some thoughts.

Air cleaner plugged? Throttle cable not advancing all the way? Bad tach?

don't forget the filter at the carb inlet....if you still have Q-jet's

Is this a normally aspirated engine with a 4-barrel carb?

If it has vacuum secondaries (likely) then I would verify that they are opening. Look for linkage problems, sticky butterflies, or other problems with the actuator. Usually it is an easy fix and they just get sticky due to lack of use and "gunk".

If the secondaries don't open the engine will usually run smoothly, it just won't make WOT power or RPM. Happens on the `Vette once in a while.

Look down the throat of the carb while advancing the throttle by hand (engine not running). If the secondaries (second set of butterflies) open when you get close to full throttle, then they are mechanical. If they stay closed, then they are actuated by a vacuum device.

I would be very, very, very surprised if your engine had mechanical secondaries.... vacuum is the norm.

Replace fuel pump that what it sounds like.

Really??? What carb you running on that thing?

Probably a Rochester Quadrajet.... a very common carb for the 454 (and smaller engines).

In reality, the Rochester does have vacuum operated secondaries. The large butterfly plate above the mechanical secondary butterflies is actuated by airflow and engine vacuum. If it is not operating freely and properly the secondaries won't "work", even if the mechanical butterflies open. Common issue with the Q'jet.

Vacuum secondaries on marine engines are quite common. All of my non-fuel-injected engines have had them.

Wow...I'd get me another Mech...I've never seen Q-jets without Vacuum secondaries. But if both filters are clean then I'd check the pump.

I would get a good mechanic that can diagnose the problem and not just a parts changer. Have you checked fuel pressure under load? Have you checked ignition timing and advance? Spark arrestor? etc etc etc......