Non accelerating vehicle

We bought this vehicle yesterday.  It ran great yesterday
and today when I was driving the vehicle wouldn't
accelerate very fast while taking off from a stop sign.  It felt
like it was running out of gas where it would take off for a
few seconds and then not accelerate again, even though
the pedal was pressed to the floor.  The gas tank was on
full and when accelerating to would jump to a half a tank
and upom stopping would jump up to a full tank again.  Any
ideas on what could cause this?