1996 Yamaha 40hp 2 stoke modal 40mlhu

I have a 40hp Yamaha 2 stoke. It ran great, took it in for service (carb cleaning and change leg oil) got it back and put it in storage until spring. The bout now has a max rpm of about 4500. I brought it back to the Yamaha dealer an said it has no power, and they sad they could not find a problem. Over the last few years I have taken it to 2 other dealers who also said it is running fine. The motor starts great, idles great, but feel's like I own a 20hp.
I checked the carbs myself, they are clean (spotless), new fuel pump, fuel filter is clean and have good and even burn on all spark plugs.

Any suggestions as to what may be limiting the RPMs