Loosen your upper tension a little? Did you preshrink the broadcloth? It still needs prewashing even though it's a blend...Have you changed your needle, & are you using a quality thread? Those are the things that come to mind along with triple checking that the machine is threaded correctly.

I'd sew on some scraps of the fabric while you monkey around with it. I find when my stitch quality is off it's almost always my needle, but I don't change them often enough.

I'm not familiar with Broadcloth, but sometimes the fabric doesn't feed evenly. If guess you don't have a walking foot? If not, do you have a teflon foot? Either one would help. Also, try holding the fabric taut, front and back while you sew, using a looser tension and a longer stitch.