If you want to push your trim tabs deeper into the water, you can put shims between the cylinder and the tab. Most tab manufacturers can supply them or you can build your own. Just make sure that the tabs will still retract to a position at least flush with the hull bottom. You can also build extensions onto your tabs. It helped my boat.
I really don't think that the trim tabs are your problem although they certainly can help to compensate for the real problems. Most of our fishing boats are stern heavy and yours may be severe with big fuel tanks at the stern. Motor height is important and I've seen lots of boats with "conservative " motor heights ( too low).
For stern heavy fishing and cruising boats where top speed is not really important, I really like 4 blade props. A properly sized 4 blade will improve hole shot, load carrying ability, cruise efficiency, slow speed (rough water) performance and do it all at lower rpm.
Good luck with your boat. A few changes can sometimes make it "a whole different boat" and result in more enjoyable cruising.