Have you tried using your machine in manual mode at all? I've had my Queen Quilter for just over two years and also had tons of issues with tension and thread breaking. I was about to call a repairman a few weeks ago and decided to switch from my stitch regulator to manual to see if there was any difference hoping that it would narrow down my problem. While I prefer the stitch regulator in theory, I had no problems at all in manual mode. I did have to tighten up my upper tension quite a bit at first, but have now quilted 3 quilts in manual mode without any tension issues or thread breakage. (Of course I will now be jinxed after writing this!) I recently bought a K-Kraft Bobbin winder as well, because the one on top of my machine was not working well. I love having this bobbin winder. A few of the down-sides to using my machine in manual mode are that I need to be consistent in the speed I move around the quilt to keep my stitches relatively the same size. Also need to be quick on the trigger finger to stop the stitching when I stop moving the machine.
As far as my tension issues in the stitch regulator mode, I'm figuring it's one or both of the following problems: My encoders could be bad, or they just don't make good conduct with the pipes. My conduit pipes have a slightly rough texture to them as opposed to being smooth as glass. Home Depot only carried one kind that would work for me when we did our set up. I'm guessing the encoders may have difficulty rolling over this rough textured surface and translating that information to my stitch regulator.