2006 Yamaha 150 sluggish

[jimgeoko]

I have a 2006 150 Yamaha on an Azure deckboat. Starts fine but the last few times I've taken it out when I open it up it will do fine for a minute or so then gradually slow down. It won't turn completely off, just won't go back to full speed. Somewhat back and forth, even to the point of almost losing plane. Runs find at idle and slow speeds. (I have it on a lift and it takes me about 20 minutes to get where I can go full speed.) Have had it serviced regularly and had my local repair guy come out and he said he didn't know what the problem was and suggested I take it to someone with a diagnostic computer. Any thoughts appreciated.
Jim

[rodbolt17]

if I was more ambitious I would look up how many models of a 150 HP motor Yamaha produced in 2006.
but I am not so Ill wait for a model number to appear.

[jimgeoko]

Sorry. F150TXR.

[jimgeoko]

And now that I look at the paperwork it was a 2005.