The GEVO TIER IV ET44AC, also known as the intermountain unit, is an industrial. This unit is powered by 6 axle High adhesion trucks that are powered by alternating current. This is the first model to meet Tier 4 emission standards by reducing emissions by 70% below tier 3 standards. There are some small modifications made to this unit that are visibly noticable including a larger radiator for cooling, modified exhaust stack housing unit, suppressed compressor, updated cab features using railconnect 360. It was introduced in 2015 and is now operated by all Class 1 Railroads.

Many are in service Pulling mixed goods, intermodal, tanktrains and spine cars.