2003 225hp Boggs out after 4000 rpm

I own a 2003 Yamaha F-225. Since Yamaha put a new block in under warranty two years ago, I have had fuel related issues. I have had it at two local authorized yammi dealers and thay have changed everything pertaining to fuel on the boat except the fuel tank (it has been cleaned though) I also have new plugs (3 times), new fuel pumps (two of each), new fuel lines, filters, primer bulb (changed twice), water seperator. No one can seem to figure this out. I am wondering if there is a problem with the head at this point because there seems to be no explanation. I haved poured more money into this motor than it's worth at this point and it only has 450 original hours. 20 hrs since the new block. Sometimes the boat will run fine at full throttle, but it wont idle without pumping the primer bulb. This year it won't run at all past 4000 rpm's. I can't jump on plane but if I ease the throttle, it will plane but takes forever and like I said I can't throttle past 4000 rpm or it wants to shut off. Please if anyone can help me with this I would greatly appreciate it. Yamaha won't do anything about it because the warranty is out even though it has never run properly since they put in the new block. It hurts to have $45000 rotting in the driveway every year. Please help. Thank you, Rob