I would suggest the plane in question needs a proper service, bose-x
TWO INCHES of MP is a big power difference. I've just looked up the IO540-C sea level performance and say 25" v. 23" at 2575 is about 20HP at 190HP, and a similar 20HP difference at lower or higher MP levels. If you get the same RPM on both engines with this much thrust difference then the prop governor needs some serious adjusting.
Also, the fuel flow difference would be obvious - if you have a flowmeter on each engine, and if you haven't, we are back to guessing what is in the tank.
read the post IO, I did not mention manifold pressure I said LEVER POSITION.