You might change the needle again. Sometimes they are mis-manufactured and have a little burr that can cause problems. The repairman who maintains my machines says that about 10 percent of needles are defective. And check to be sure that the needle is inserted correctly and that the needle is inserted all the way. A tiny bit of deviation with the needle can cause some real headaches.
My sympathies with your stitch problem. It can be soooooo frustrating!!!!