Generally,Coors has a dramatic (negative) impact on range and zone ratings, so that could be your explanation there.
Additionally, it's my recollection that a number of defensive stats seem to be inconsistent from year to year. (Not just PB stats, any metric). I think this is because individual defensive stats are so dependent on other players. If the team gives more starts to a couple of ground-ball pitchers and less to a high-K starter, infielder range factors will go up. If there is a poor second-baseman getting more starts, DPs will go down and with them assists and with them range ratings.