AM back to your post /description above.
You have a 25" leg on a 20" transom...
Which makes the prop and cav plate way too deep.
And althu some of the effects are similar to others .. assuming their height is correct, the reasons are very different.
You cant source a engine for a while...
Actually fixing the issue.. lifting the motor to where it and the hull are designed to work at together will make a completely new boat.. I emphasis .. completely Bottom line 25" 0n a 20" transom will not , will never work by messing wirh angles etc
Trim tabs will help a little, but not worth doing the capital investment
A Foils may also help but will not be worth the effort...And each of the above will just add to fuel bill
ONLY economic and practical fixes fix
is increasing transom height
or a engine jack
Transome height..
Can get it rebuilt..expensive
Can get a wide plate made up that covers the transome below the engine well..and up higher,and back down into the engine well inside...
Engine jack..
these range from around $350 to $700 and more for fully adjustable.. or can make up some yourself out of suitable U sections.
When calc required height it is important that you also factor in the angle of the transom.. if you do not then you will not get correct height.. even if adjustable.
Once you have engine height correct, all .. everyone of your issues, loading , weights economy, hole shot will evaporate.
From there it will just be selecting a ball park prop and have a totally new well performing boat.
There are more detailed instruction in old threads on engine jacks, measurements, etc.
If any questions please ask anyway
I only hit the web once a day, brefly most days
PS when we repowered our 5.5m 1250 gross weight commander from min well powered 115hp to intended well powered V6 140hp.. my issue was the engine leg...to source a late model 20" is like hens teeth on mars.
Took 3 yrs... eventually ending up with a far heavier V6 150hp 2s
The only , and not an issue, is at anchor sits a couple inches deeper in the water.
If a boat around this sized hull, height correct and prop in ball park well powered, be it min well powered, engine to very well powered, putting an extra 20L container of water near the stern, or a person sitting back there will make no to very little noticeable difference to what the hull does .. hole shot to economy to performance in chop etc.
As to all the mainline brands.. merc, suzi, mariner, yammy, honda etc. new engines have yet to sort their long term issues.
Long term issues on older models are in most cases sorted.. If me , I would buy ex my local workshop that I have had yrs of service and faith in. If not available, then go a little further afield , but still in easy transportable distance.
And if nothing, since what you have is around min well powered I would be engine jack/ transom, with chances being very likely not bothering to re power...PS if you got advice to do stuff like change engine angles to fix the issue of 25" leg on 20" transom..
well I shake my head in total astonishment it would even be mentioned over actually fixing such a major ,core issue problem... or as a temp patch up fix.