Some thoughts...
Do you have an adjustment on your machine that controls the pressure on the foot? Loosening that may help. And be sure your feed dogs are lowered. Is there a spring on your darning foot? There should be a little bar or something that likely is positioned over the screw that holds your needle in. I had to bend that part on my darning foot so that it would lift the foot higher on the upstroke so that I could easily move the quilt sandwich.
Also, how thick are your quilt sandwiches? What type and how many layers of batting are you using?
A picture of the foot would be helpful in trying to give you good advice here.