Put some more deadzone on your analog stick for slewing.
If you have the JHMC on and selected and you slew analog switch can "Twitch" from the center it will move it to where you're looking, so put some more deadzone on your slew stick.
Try moving your TGP while looking around with helmet mounted system and move the Slew stick, you'll see what I mean.
Or make anything else other then your JHMC as SOI when you're going for attack