1 or 2 degrees in 30 seconds (for heading) is more than I would expect. After calibration, roll and pitch will usually change and then stabilize as the inertial sensor is generally not mounted perfectly flat, however, I would expect to only see perhaps 0.1 degree drift in heading after 30 seconds. You could try performing a full factory cal, that’s more to do with absolute roll and pitch values, but it may help.