I was driving last night in the snow like 1/2'' packed in 2wd. well i was cruising at 45 and my drive-train bumps or gets interrupted for a second then its normal. It only happened on snow not on bare asphalt. are the rear tires getting loose then hooking back up? It does not happen in 4 High in the snow only in 2wd

04 xlt 4L 4x4