ccbear, I'm going to start my comment with a caution - the following is not for the faint of heart LOL
You're not the only one who has experienced tension problems on these machines. I have the non-Disney version of this machine, the 700. I've had the same tension issues that you've had, and none of the machine adjustments have helped. First, I bought a spare bobbin case so I had one set-at-the-factory in case I messed up big time :D Then I took a screwdriver to my bobbin case and adjusted it for the pre-wounds I use all the time. (I get my pre-wounds from kittyshack.) I still have to adjust on the machine if I change threads, but it works much better now. If you don't want to buy another bobbin case, you can mark your bobbin case where the screw is now. I have to tell you, I've never had to put that spare bobbin case in the machine.