I would check your controller and make sure your throttle is registering 100% input. The trigger buttons are the DS4's weak point. the HUD has a throttle input bar. Make sure it's getting filled.
Controller is all good. I have no trouble with any other races, it must definitely be something I'm doing strategy-wise. I was in 2nd when leader pitted but he wasn't there long enough for me to overtake. Going to have to waste another hour of my life doing it again I guess. Won't hurt to turn down to TC1 too.