A stallguard value of 1 generally s not satisfactory for detection of a stall. You would have to increase velocity in a given application to get a higher and stable reading. You could try filtering using TMCL, but this will reduce the exactness of the stall detection, i.e. higher response time.
To get the maximum StallGuard reading with the 310, please be sure to use a 1A RMS motor like the QSH4218 series and drive it at maximum current with mixed decay turned off.