What default flight do you have?
Have you tried setting your default flight back to THE default flight? The one that comes with the sim? The trike over Friday Harbour.
Resetting your default flight to that quite frequently solves many, many problems. It set all the aircraft.cfg, .air, sim, and gauge variables to the proper defaults. They can often get somewhat screwed up by addons, especially if the default flight you're using utilizes the add-on for it's plane.
Try resetting the default flight to what the sim came with. It's pretty easy to do in the FSX.cfg file. I just recently wrote up an easy to follow "how-to" for another guy. I can copy it over here if you need me to, or you can just do a search for my posts in the FSX:SE Problems forum.
Anyway, just a thought...
Pat☺