54' Offshore won't get on plane

A friend has owned this boat for approx 3-4 yrs. The boat has C18 Cats 700hp ea and about two months ago it would not get up on plane. Its a relatively slow boat and when on plane about 14 knts. Bob from Cat came over about a month ago and said its not an engine problem it was likely props. Thats when owner had boat pulled and all the bottom work done. The bottom was painted, new cutlass bearings, props pulled & scanned by General Prop, rudder and trim tabs both check okay. Put back in water and still same problem. The engines will get up to 2200+rpm and boat will be struggling trying to get on plane. Any ideas on what the issue could be.

I'll try to answer some of the questions.
Bayoubud you are correct they are C12s. My mistake. The max rpm is 2300 and they will turn that I was just saying it wasn't planning at 2200. We didn't go any higher.
Beau the problem did arise all of a sudden. The boat has been in the water since he owned it other than for a haul out once or twice. Trips to Keys & Bahamas last two years. The owner has not changed anything.
NYCAP - other than the recent haulout the bottom was also painted last year. Guess it could be water in the hull although for it just to appear all of a sudden is strange. Its a 2003 boat. No known blisters.
Pascal - the scale was broke when boat was hauled so we did not have the weight. Suspect around 80k. In order for the boat to plane the tabs have always had to be all the way down.

NYCAP agree on the tabs although alot of pressure was applied when they were down as well as up. Fluid is full. I believe that weight for dry hull is correct. With 1000 gal fuel, 300 gal water and extra 25kw generator and alot of misc it is a heavy boat.
Capt Ralph - before the issue the load was 80% at 2000 rpm. Since the problem the load is actually about the same maybe slightly better at 76% since the props were scanned and balanced. Don't have any fuel flow data.

When we ran the boat yesterday after getting it out of the boatyard it did the same thing it was doing when we took it in with the problem. Up until this problem the boat has been run weekly to keep the bottom clean when this issue developed.

PacBlue - no its not the bottom paint it did it before it was hauled and repainted. Yes we ran ran it outside and inside trying to get on plane. On the props it did it before and then after the props were scanned. They were scanned and tuned after the haul out but the problem started previously before this was done.

Capt J it has always been able to plane at 14 knts with trims full down. He runs it in the intracoastal as well as offshore at 14 knots. The boat now when trying to get up will start shuddering when it gets close to that plan speed. Kind of like you would have an prop with a bent blade except rpms and load are pretty normal.

He spoke to someone late yesterday from Offshore and they told him to check a section of the hull for water. Supposedly there is a pocket on the outward side of the hull that water could leak into when filing water tank.
Thanks for all the feedback will let everyone know when the issue is found.

Yes it is.