Banelings!

As a high gold who recently realized that his TvZ sucks and then got together with his practice partners to fix it, maybe I can help. :D

When it comes to attacking Zerg early, you really have to move cautiously, and can't be caught unsieged. Leapfrog forward with you marines spread into even two or three groups - siege a tank, while moving the other forward - and banelings will be easier to deal with. This may seem slow and ridiculous, but it's amazing how much better your engagements will go. 

If you have medivacs and tanks at the same time, an early two-pronged assault can be VERY powerful. So maybe do that. 

With practice, your control will improve! Mine did, at least.