Which model sniper did you get? The "normal" one has 4x 100lb/hr injectors.
I suspect you are falling off the bottom of linearity map for the injectors at that rpm/afr.
Next time you are messing with it, keep and eye on both the AFR and the Pulse Width while it is jerking.
I suspect you will find the pulse width is falling under 1.5mS and the AFR is going really lean before recovering and the jerkiness is it flopping back and forth between really lean and significantly richer than you target.
If so, I have a couple solutions to propose. If you are not seeing those symptoms, I don't want to muddy the water with unrelated suggestions.
