New Upper. Cant get on plane

[Hawkrdr]

I have now gone through 2 uppers in a matter of a month.
I am running a Merc 5.0 MPI 260HP on a 2004 Monterey Montura 248LS.
Thies boat is 4900 lbs dry and has a 80 gallon fuel capacity with a 20 gallon fresh water system as well. (heavy boat)
I was originally running 1.62 upper when the first one failed. I replaced this with another 1.62 upper from SEI. First time I was able to go to full throttle, the gears failed again.
On a recommendation of the tech I was given a 1.47 gear ratio upper.
Now that I am through the initial break in of 5 hours I tried to get up on plane to get to 3500 RPMS and I could not climb past 2800 RPMS and never could get on plane.

I am running a 15 inch 19 pitch 3 blade stainless prop. I see no way I could re-pitch to gain back almost 2000 Rpms.
The operating range for this boat is 4500-5000 RPMs at WOT.
Any help or info would be great on this.
This is getting exhausting replacing the drive every flippin 3 weeks.....

[admin]

With the ratio change, you will definately need to reprop. I went to an online prop selector and punched in your specs. It is recommending anywhere from a 14 pitch to a 16 pitch prop. I would suggest going to Mercury Marine's website and checking it for yourself. They have a couple ways of selecting the best prop.

Tech Support

[Hawkrdr]

I have picked up a 15/15 prop and will be trying this to see if I can get it back into range. I will update when I find out.

Thank you.

[Hawkrdr]

Well, the 15.25x15 worked like a charm. Never did go full throttle but popped right up on plane and comfortably cruised at 3100RPMs pushing between 25-28 MPH.
1/2 tank of gas, 2 adults and 2 kids.. Not quite the load I had last time out but it responds like it should now. Now if I can just keep it running we will be good to go.