Sitkaquilter

Hi All, it's been a long time since I've posted anything here, but I do follow new and seasoned friends daily.
I indulged myself upon retirement with a QE 4.2, which sees beautifully, both simple and fancy stitches. However......I am having endless problems with the free motion function, such as loose bobbin tension, skipped stitches, and loose bobbin winding mechanism. I've taken it to the shop three or four times now. They give it a tune up and, for about ten minutes, it free motions beautifully. Then the problems return.
Have any of you experienced this with this machine?

Thanks for any input.
Jeanette - newly returned to WA state after years in Alaska.