I took my machine in today, and now it's back home. I took my stitch samples on various fabrics in today along with my machine. Their test samples right in front of me were perfect. So what's the deal?
I've been using the new dual duty Coats&Clark a lot, probably for about a year. I purchased a lot of spools in black, white, and beige when they were on sale at Hancock's a while back. Come to think of it, that's about how long I've been having tension issues. My machine doesn't seem to like that new thread. I thought it would be better, as in "new and improved". Well, maybe it is, but not for my machine. They highly recommended Mettler. Same price as the Coats&Clark with my lifetime dealer discount. I know C&C is not a recommended brand for serious sewers, but it has always worked for me in the past. Doesn't seem to be anymore with the new spools.
So, I bought several rolls of Mettler. So far, so good. I need to get another 6 years out of this machine :) .