Mine dances too but I only notice it when 1/2 tank or below. It's about time for some injector cleaner anyway. Hopefully that'll help.
On every other vehicle I've owned, the first 1/4 tank of gas lasted alot longer than the last 1/4. The VX appears opposite. It comes off full very quickly but the last 1/2 tanks seems to last forever. I guess it's all tied together.