Having a problem getting on plane

[Divine Comedy II]

2004 280 Sundancer at low rpms the boat runs fine, usually get on plane at 3000 to 3100 rpm. Noticed that throttles are no responsive enough when pivoting and docking and throttling up. The cables have been adjusted numerous times, and getting worse. The boat just before getting on plane experiences cavitation at an rpm well below the normal rpms needed to get on plane. It now takes a much higher rpm to get the boat on plane. All of this has been tried in varying wind conditions with the same result. We cleaned the props and buildup on the back of the boat so we do not think that a dirty bottom is the problem.
Wondering if we have 2 fold problem. Bad trottle cable or bad engine. 7 days prior we put in 50 gallons of gas at a new gas dock that has a lot of turnover, and then the boat sat for a week. Prior to gasing up the boat ran fine with the exception of the non-responsive throttle.
Any ideas?

 

[Hampton]

What kind of drives? I'm not an expert, but it sounds like you may have a prop hub slippping which allows the engine to rev but the prop does not turn up to speed. Are these outdrives? Are they trimmed full down and checked full down?

 

[shore]

I had a problem like this and it was a drive was not down all the way.The gauge said down but it was trimmed up..prop blowout was my 1st clue.