1996 250 Yamaha no power help!

Sir I really don't know what to do. I have 1996 250 Yamaha outboard that I bought about 7 months ago. The first time I went out about 50 miles and it ran good! But after fishing for a few hours, went to go home, and instead of 4700rpm it only ran wide open at 2700rpm! I let it sit 2 or 3 hours and still ran the same. Since then I have drained all the gas, put in new plugs, and cleaned carbs, checked fuel pumps (3) and none are not leaking, changed the TPS. The lower unit oil is clean, no water or metal. I've checked and cleaned all grounds, oil pumps (2),(one on boat and one on motor) are working good. Now it will run good for about 30 min or so then its back to only 2700 rpm tops. don't know what to do next..Any suggestions??

[offshoremadman]

sounds like a fuel issue, I have the same motors one had a similar problem, replaced the lp pumps has ran fine every since,
from what I have been told they need to be replaced every few years.....