Have you cleaned between the upper tension discs? If there is a tiny piece of thread or some lint stuck there, it will suddenly change your tension. Best way to clean it is to open it all the way out (setting of 0 is the loosest) and then use *unwaxed* dental floss all around between the two tension discs. (If you look closely, you may be able to see the tension discs. They are what tighten up to put tension on the thread when you dial to a higher number.)
The other thing I wonder about is a tiny piece of thread caught somewhere in the bobbin area. It can be hard to see if it's just a small piece of thread, but still can wreak havoc with your tension.
Did the tension change on you before you switched needles? If so, I wouldn't think it was the needle that caused the original problem.