Gallbladder removed by kh 3wks ago. have pulling sensation and hard lump under top incision. can't stretch fully as it pulls. should i be concerned?

Likely normal: I do not know what size incision or port size you had placed. Tightness, soreness & firmness at a surgical scar will last 4-6 weeks or more. Probably normal. See your surgeon for an exam to be sure it is healing properly.

Maybe: Most likely everything is fine but you should make an appointment with your surgeon for a post op visit to make sure. The possibilities include scar tissue forming from surgery, a hematoma (or tissue blood clot from the trocar), an infection, or a hernia to name a few. Your surgeon should be able to advise you and make recommendations to get this lump to resolve.