True single engine ceiling on P337?

[kevin]

I received this inquiry today:

Sir: I've always been under the impression that the Pressurized Skymaster would hold altitude at nearly 18,000 feet one only one engine.

Either the front or rear. Recently we had an experience while flying with the front engine off where it lost altitude from 8,000 feet. What is your experience in this matter? I think the book states that the ceiling using the rear engine is much higher than that. Rear engine seems to be developing the right amount of power and gets similar performance out of the prop.

Where would you look for a problem?

Any help is greatly appreciated.

Mark