I bought the motor new with my boat. It has always run great with no issues; however, lately she will not run out on top end. Put it in the shop, they found water leaking into cowling from 2 different hoses. Ran great when I picked it up, was at Falcon yesterday running up the lake for about 2+ miles and she starts slowing down again. She does not quit, she just drops from 72 down to 66mph or so if I keep my foot in it like usual do. Then I back off on the gas down to 4500rpms or so and she runs fine, I can hammer down again and she may or may not get back up to top end again and if she does she will start to slow down again after a minute or so?????

Any ideas, suggestions would be greatly appreciated...

Sounds like low fuel pressure to me but I'm not a mechanic, just an old racer. Could be a pump losing pressure, a hose restriction, no vent on gas tank, ect.

Jimmy, thank you for responding. I thought it would be a restriction as well. I thought of replacing all the fuel lines. I replaced the 2 fuel filters and spark plugs too; but, it did not help. A friend told me today to put seafoam in my tanks too as I may have some water in there even though I use stabil and ring free.???

Fuel pump diaphragms or the other 2 fuel filters you didn't replace.

Sea Foam will not hurt anything so go for it. It sounds like fuel demand of some kind but I may be all wet. LOL I would look at all the filters and pumps for sure then blow air back through the line at the bulb back in to the tank and make sure it is open good. Look at the bulb also. It has a check valve in it that could be bad. While going down the lake can you reach back and pump the bulb, if so get your passenger to help and see if that makes a difference.

Do not try to blow air through the line back to the tank, all boats have an anti-syphon valve at the fuel tank outlet connection. Most likely manual fuel pump diaphragms or the high pressure electric fuel pump strainer. Have the hidden fuel strainers cleaned or changed. See post about them here or Iboats. Clean the O2 sensor too.

i'm going thru my 200 hpdi filters now, this is the second time in 12 yrs i've had to do it. it would take too long for me to explain all the hpdi fuel problems. the best way is to google "hpdi mystery filters". it's not rocket science,but a little complicated. good luck.

Thank you all for the replies, I will start looking into each one of them...