How do I fix upper thread tension being too high? Recently my sewing machine (Brother CS6000i) has started acting up, such that the lower stitches are pulled through to the top, and the top thread is so taut that the fabric puckers or bunches up. I was able to un-gather the fabric every few inches by pulling more thread through, but that's far from an ideal solution.

It seems like the tension on the upper thread is way too high. If I try to gently pull the thread through the needle, for instance, it takes much more force than usual. However, I hadn't changed my tension dial before this started happening, and cycling through the settings didn't seem to make a difference. This is happening consistently and on all fabric types.

When it first started, I swept out and jiggled various things, which got it working again for a short time, but since then no luck.

Any idea how to fix this issue? Do I need to get it serviced?
Are you using the correct needle point and size for the fabric? 


Ball points for knits 
Straight points for woven fabric


Sometimes the needle just needs to be changed.

The other problem could be the thread holder, are you using a spool or cone? How is it attached or docked to your machine or the table?  
 
If it is a spool that is loaded sideways, the thread might be getting caught in the spool's edges and you just need the slide on piece (spool cap) that holds the spool in place. This may also help on a vertical holder.   

If you are using a cone, check to see if the thread is not releasing, sometimes it can get caught up underneath. You may want to get a spool holder and mount it to your table near the back of the machine.