Switching to more efficient might sound like a good idea until you really sit down and figure out the cost benefit. It's way cheaper to feed in more gas $$$$ over the long term unless you plant to keep it for let's say 50 years. Maybe then you will break even. Good luck.

8.1 isn't really the big brother to the LS, still runs BBC head. Really nothing like like a LS actually. lol

At 3k I'm roughly 30% throttle. This isn't a offshore boat and your going to laugh when I tell you but we all start somewhere. Its a 25ft pontoon and the motor is a ls 5.3l with twin turbos. Will run really close to 70mph at Wot.

Just because you are running a lower rpm does not mean you will use less fuel. An increase in pitch will more load on the engine.
Its like going from level ground driving a car and then going up hill. You have to give it more gas to maintain your speed and rpms.

I'm pretty happy if gas is the only thing I buy in a season.

New outdrive = 2 or 3 seasons of gas money
New motor = 4 or 5 seasons of gas money