It could be the drive motor too. SOmetimes you can swap them from side to side and see if the problem moves.
As you say track, i assume this is a tracked machine? if so, the sticking could be from the reuction box, a part of a gear could be floating around sticking between other teeth. If this is the case, you need to get into it sooner than later. The longer it goes on, the more damage it will do.
