Check your Drive Alignment , Engine Bed Might have settled. Swap Drives , if it doesn't move . Swap Engines see if it moves .

no adjusting with offshore mounts, drives slide right in no issues...

check voltages running on hose all over, both engines identical, now going across waves in lake I have no way to check besides dash gauge that reads same as other, engines dynod with alternators and sea pumps.

Do you now leave fenders hanging off this side of the boat.

I had t realized how much time had lapsed between dyno and run time. PLUS you mentioned they were reasonably close to identacle RPM's "in boat" and then now this.

omg that MUST be it!! LOLOL

I think next step for chits and giggles is to swap distributors (msd ready to run) so all ignition is in that, just in case for some reason it acts up under way in boat and did not on Dyno, if that is not it, the coil is next, then if that's not it... going to run direct wiring from ign. switch directly to distributor bypassing my engine harness, On dyno we direct wired dist. we did not use my engine harness for power to ign. that's where I am starting next...

built engines and put into boat last june, ran good for a few weekends same rpm, then a drop on port I noticed, played with it last summer a little no changes, was happy to be boating, pulled over winter to dyno and replace a bad trans, engines dyno identical, put in boat still have rpm drop, fast forward to now lol

How did mild not talk you into new programable distributors.

Went back and read original thread. I misread the dyno'd after noticed rpm loss with run time. This is a real beiotch. Swap drives or swap engines. Or lose more hair mean while. So to date did you do the coil swap including ign box?