My 2003 Baja 275 with a 496 HO and a 25 pitch prop used to go 67 MPH on GPS at 4800 RPM but now it goes 63 MPH at 4500 RPM, what happened?

It slowed down.

When was "used to"? What has changed since then? Weather? When did you last change fuel filters? Have you ever cleaned screen in cool fuel assy? A lot of experienced minds on OSO, you need to give more info.

Sorry but I didn't do anything. It ran 67 mph 4 weeks ago on the Ohio river hear in Cincinnati and now it doesn't. I have not cleaned the screen in the cool fuel assy. I don't even know where that is. Sorry I am new to this boat and engine, we got it 8 weeks ago. Any help would be appreciated.

Gas without ethanol compared to gas with ethanol? Mine runs a lot better without alcohol.

Air temp, humidity, river current, and amount of fuel and people could easily account for that loss in mph.

If it sets in the water a dirty bottom would do it.

Thanks guys I think my fuel filter is suspect. I did put some Lucas injected cleaner in there a probably clogged the screen. The bottom is clean, I know the boat goes faster on the GPS downstream with a fast current. I know weight effects max speed.
I bought a new filter and screen today I'll let you know.
Thanks again and maybe I'll see you at the lake Cumberland raft up August 10th.

Guardian mode
Does it beep twice at key turn?

I will check.

Up river vs down river??