I have noticed when on full heat (engine warm) the highest fan motor speed barely blows out of the front ducts. Back is not on and vents are set for full front. When on high with the air it blows hard. It seems to warm up ok inside but you have to hold your hand on the vent to feel the air. I've heard other later model Toyotas are similar. Coming from a 2013 Tacoma its a vast difference. Maybe it's a feature not a bug.