2007 Merc 25HO EFI 4 Stroke RPM issuse - i believe it is

[AC2717]

Hi guys, I have a 2007 Mercury 25Hp EFI 4 stroke - serial#: 0R181035

When I am just reving the engine with just throttle (button pushed not in gear) it revs up nice and high and wants to scream at WOT (basically runs great) when I put it in gear and try to WOT it, the motor barely does about a quarter of what it does when it is not in gear at WOT.
Does anyone have any idea why this would happen? Is there something electrical when in gear like a Limp mode? Is it the load from the lower end unit? Also I had to have the lower unit rebuilt, would this have anything to do with it? gear ratio or anything under load, but from what I found there is only one set of gear ratio for these lower ends 1:92:1

I am running stainless 10 inch diameter with a 11 pitch on it, I know the prop changes performance. The engine is guesstimating to not even get up to 1500rpms when in Gear with WOT and it is not bogging down or anything. it won't let itself go past that rpms

I have had the throttle linkage adjusted and checked and in gear and while just throttle, the throttle linkage moves to the same exact spot so it is not losing traveler distance when in gear
Thank you in advance for ideas

 

[alldodge]

Not an OB guy but

Reving a motor in neutral tells nothing about the motor, it takes very little fuel to do it.

The engine is guesstimating to not even get up to 1500rpms when in Gear with WOT and it is not bogging down or anything

I would check fuel pressure and see if it drops when under load

Why was the lower unit rebuilt?
Were there any issues with the motor prior to lower being rebuilt?

 

[AC2717]

it failed while underway from the previous owner. No issues prior to being rebuilt