A couple weeks ago my flame wasn't as high as it normally was. Take the clip that holds the gas hose to burner off and remove the gas hose. Unscrew the brass fitting off the gas hose and take some steel wool and clean all the built up ash/gunk around the pin hole where the gas comes out. Take a safety pin and make sure the little hole is open where the gas comes out. The burner tube also gets charcoal ash built up in the end on the grill side, blow it out, put back together and see if that helps.
If that don't help I would think the regulator may be going bad.