A transmission system constructed in accordance to one example of the present disclosure includes an aftertreatment system and a controller. The transmission system is selectively coupled to an engine crankshaft of an internal combustion engine arranged on a vehicle. The aftertreatment system reduces emissions in an exhaust of the internal combustion engine. The controller operates in an aftertreatment heat-up mode such that the aftertreatment system is heated up to an elevated temperature and emissions are thereby reduced based on the elevated temperature. The controller operates in the aftertreatment heat-up mode when the internal combustion engine is operating at or below a brake mean effective pressure between three and four bar. The aftertreatment heat-up mode comprises increasing load on the internal combustion engine.