Mine does it too. I feel too that the fuel slosh is b.s. It some times does it & some times doesn't. Some times on a 1/4 tank some times full. I believe that it's a drive train issue. I.E: the torque converter binding, the rear diff twitching under break load or release or torque load. Or it's the pinion having too much slack or the transmission thinking it's still engaged. I dunno but it's annoying cause it makes me feel uneasy about the quality of the drivetrain in my truck. If anyone ever gets a handle on this issue I'd love a courtesy post/ update.