Maybe the problem has to do with riding technique. You used to ride a 26er but now you're riding a 29er. I would guess that the bikes have different geometries and different vertical & horizontal centers of gravity. If that is right, your riding technique may need to be changed somewhat for the new bike. For example, it might require a lot more forceful body english to keep the bike (with those larger heavier wheels) on track, or it might be a matter of shifting your body position more radically than with the 26er.