97 225 venom

[xxxdan1]

Ok need some help here, Last year replaced lower unit on motor and this is were all my problems started. Prior to the new unit i was runnin about 5800 rpm @ 67 mph with a 24p raker Now with new unit turning 5000 rpm @ 54-55Mph.. Ok ive changed props several times no luck. hell i put a 19p on just to see if i could get back to 5800 no luck so my question is wtf could be the problem been through lower unit all is identical to old 1 gearing and all is same,did a leak down test all was good there compression was good complete tuneup all runs good just wont go past that 5000 rpm mark.