2001 50hp 4stroke wil not run over 2300 rpm.

[bitsy4643]

2001 4 stroke mercury, 200 psi all cylinders, will not go above 2300 rpms. Mechanic assured it was carb problem, paid 500 dollars for carb rebuild, runs worse now than when took to him. I have carb tune tool, carbs were badly out of tune when returned. Upon retuning motor runs fine until 2300 rpms. Same problem as before. Have replaced oil sensor, ecm, water pump. Same problem. Oil pressure is 60 psi. Is that not too much, could this have an effect for not reaching rpms? Motor starts immediately and idles perfectly. I have posted here before, but have been unable to find a solution and cannot find a mechanic that I am confident can fix problem without replacing parts. Could this be a timing problem? Any help, suggestions , or ideas will be greatly appreciated.