I have a 2015 920 Phoenix with 250 Show Yamaha. Going about 65mph I'm getting about 4000 RPM's. Is that right or should I be getting more?

RPMs don't get associated with any particular boat. For any given boat/motor/prop combination, the proper prop should be selected. The rig should be propped so that the engine runs just at the maximum engine-manufacturer approved RPMs. Generally speaking, if the pitch of a prop is too low for a boat, the engine will over-rev the RPMs and the rev-limiter will kick in. For a prop with pitch too high, the engine will bog down and never achieve the power rating intended by the manufacturer. That power level depends on reaching the max RPM.

I don't know what the max RPM is for your particular engine, but most SHO's state 5000-6000 RPM as the max power range, so you appear to be WAY out of line at 4000 RPM. You are either grossly mis-propped, have an improper engine height, or a mechanical issue. The proper prop on that boat should allow a 250 SHO to run 5000+ RPM.

Could be the tach.

If you are running 4000 rpm at wide open throttle trimmed up with the boat running 70 something mph then you have a tach issue. If it is doing none or only part of what I just mentioned then give me a call and either me or stve will help you figure out if you need a prop shop or a mechanic.

4000 Rpm's at 65 mph? Something isn't adding up or that is one fast boat. I would get the tach checked like stated above.

I took it back into fun and sun and they supposed to have replaced the Tach but I have run it a week and still running no more then 4000 rpm's.

Something is wrong. At 4000 rpms @ 65 mph your prop would have to be thirty something to be right. If you are doing 65 GPS you must be doing at least in the low 5000 rpm's.

I have a 921 with a 250 SHO and at 70 I am turning around 5500

Yea, that's 65GPS and not over 4000RPM's