I just had my LU replaced on my 150 Optimax. The technician told me when I dropped it off to him that he would pull the broke LU off, verify the gear ratio and order the correct one....
I got it back today, put it on the water and the water pressure was really low on plane, and I could only give it about 3/4 throttle fully trimmed and the RPM alarm would go off as I was well over 6000 RPM's. I put the boat on the trailer, dropped the JP an inch and a half, put it back on the water and still the same performance. Dropped the JP another 1.5 inches (as low as I could take it) and I still take it over RPM's when fully trimmed, but not nearly as easy. I didn't have a tape measure with me to be exact, but I would guess that I'm sitting at 4" below pad right now and still not getting much water pressure and over revving.... The prop is a Tempest 23...

Why would a LU replacement have my performance so different??? What is my next move???

Also posted this in the Mercury forum...