Many Class 1 roads were already replacing SWs and MP15s with GPs and SDs twenty years ago when it became obvious that dedicated switching locomotives just weren't (or soon would not be) powerful enough to meet their needs, not to mention that they couldn't be used in revenue service like the Geeps could. These days, most of the Class 1 railroads' trains are so large that a 1500 horsepower locomotive just isn't going to cut the mustard for yard work (at least not in the larger yards); there are still a few switch jobs where an SW or MP15 may be useful, but not enough (in most cases) for the Class 1 roads to really justify keeping them around when a Geep or SD can do them just as well and be useful elsewhere to boot.