gauges might be a little bit off but not that much. looks to me that you need a prop with smaller pitch to reach 4800 rpm. you will loose some top speed (2-3 knots) but you will get on plane faster and fuel consumption will go down.
had the same problem with 22 pitch props and Merc. 5.7 EFI, running 40 mph at 4000 rpm but the boat had a hard time getting on plane without trim tabs. cruising speed at 3500 rpm was 28 mph burning 48lt per hour.
changed with 20 pitch (same boat weight and gear) and the boat gets on plane right away without trim tabs, going up to 4500 rpm at 39 mph. cruising speed at 3500 rpm is now 25 mph burning 43lt per hour.
Go to your local Volvo Penta dealer and ask him for test props. He will give 2-3 sets to try and you will buy the one that suits you best. Their tech department will help you with the right pitch according to your horse power, length and weight.
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