Level Flight Problem

Good day!As my first post on the forum, I'd like to say that this site provides a wealth of information for all FS enthusiasts and real pilots alike.Here's the problem I'm experiencing in FS2004.When I am using the autopilot and have reached my desired altitude, e.g.: FL350, it appears as though the jet has about 5 degrees nose-up pitch. I am unable to trim the aircraft to level flight as each manual adjustment I make, the autopilot reverts to the nose-up flying.Has anyone else experienced this?Thank you for your help.Tony