And that's (tentatively) the plan. However, just because these Dash 8s are newer than everything else doesn't mean they won't be without issues (they're almost thirty years old themselves, and have never been rebuilt afaik), not to mention they're a whole different beast to maintain than a 40 series, something the mechanics have had years to get themselves acquainted with. Additionally, a least a handful of these incoming Dash 8s will inevitably end up in pool serivce, reducing the number of GP40s they can replace. And finally, yes, a Dash 8 can theoretically replace two GP40s. But what happens if something goes wrong? If you have a consist of four GP40s, and one dies, then you have three left to limp the train along. If you have two Dash 8s and one dies, then what? You end up with a train stuck somewhere, probably in the way of a passenger train.