It's very common for skiers going from a smaller radius ski to a longer radius GS cut ski to find themselves falling onto their inside ski. It takes a bit of time for your bodies old movement patterns to adjust to the GS ski's slower turning characteristics.
This sound familiar? You tip into the turn and put your skis on edge, but the skis just don't seem to turn. Your body is already moving inside, anticipating the skis turning like your slalom skis do, but those dang GS skis just don't come along with you. Body is moving into the turn, skis are still tracking straight ahead, and all of a sudden you're riding your inside ski.
The solution is you have to be more patient. Make your body wait for the skis to turn after you put them on edge. Don't anticipate. Begin your turns by tipping your knees into the turn first, trying to keep your pelvis over the top of your skis until the skis begin to turn. Once you start to turn then subtly let your pelvis tip into the turn too. Do that for a while, until your body figures out how the skis respond to being tipped on edge. Before you know it you'll be skiing in autopilot again, with the inside ski issue a thing of the past.