It could be so many things... I will list what I would check. If your scope is a good one and your mounts are tight, I would give that a pass at first, on the Gauntlet. 1. Check to make sure that while shooting that the barrel is not touching the fore end. 2. Take your barrel shroud off and check to see if the plastic air stripper is cracked. If not, put it back together nice and tight. 3. Check that you didn't lose an o-ring on the pellet probe. 4. If you have a chrony, check your velocity. It could be a stuck regulator washer. 5. Check every screw. I know, it is a pain.
To suddenly just start shotgunning it is usually is a scope issue though, and unless you have another handy to try, you check everything else. Besides bad mounts, or scope on the Gauntlet most people have trouble with the bottle cage fore end touching the barrel while shooting. Good luck.