The GE AC44C6M is a 4,400-horsepower (3,300 kW) diesel locomotive that was built by GE Transportation Systems, and rebuilt by GE, American Motive Power, Inc., and Norfolk Southern's Juniata and Roanoke Shops, starting in September 2015. The AC44C6M retains the 16-cylinder 7FDL-16 prime mover used in the core locomotive prior to rebuilding, but features GE's alternating current 5GEB13B7 traction motors. Externally, the rebuilds have received new wide-nosed cabs and a new front hood section of the same design as on the ES44AC, while retaining the underframe and engine and radiator compartments of the original Dash 9 units. Internally, AC44C6M features a new under-floor air conditioner, cab signals, LSL, DPU systems, PTC, and ECP braking ability, a significant technological improvement from the GE Dash 9-40C units.

Norfolk Southern Railway (NS) is a significant operator of this model. All 124 of their remaining Dash 9-40C units, numbered 8764–8888 (excluding 8798, which was wrecked in 2018) were rebuilt from 2015 to 2018 and numbered 4000-4124.^[​1] The railway plans to also upgrade all of its Dash 9–40CW units to the same standard.