I assume you have CEM enabled? Full range of pitch is capable, from 8:30 to 12:00. Depending on the situation (take off, steep dive, throttle/boost settings) it is easy to over-rev or bog down the engine. If your pitch isn't changing, either your control is set up wrong, or you don't have CEM enabled. I'd advise against setting the pitch as an axis, try keys for Increase Prop Pitch and Decrease Prop Pitch. I find with using a slider set as an axis control, the game (or maybe my stick) has a problem with identifying the proper placement of the axis for the pitch control. What I mean is, its hard to find the center spot to stop the pitch movement, sometimes, in the heat of battle, I wouldn't have set the axis back perfectly, and the propeller would continue to increase until fine (at which point I'm overrevving the engine during maneuvers) or decrease until full coarse (which leaves me with no power to accelerate). Both are potentially fatal problems you can avoid by setting keys (which I then set to a joystick hat switch).
You should have no problem setting RPM with a constant ATA within the limits of the engine power vs velocity.