I bet your warm up routine always starts with a stretch. Maybe it's shoulder rolls, neck stretch, forward flop, or a torso twist, but I bet you are neglecting to massage your tongue and jaw.
Most students I have the honor of teaching have some form of jaw and tongue tension. Most of us clench our teeth at night or during the day, when we are concentrating on a difficult task, feeling stressed, or stuck in traffic. All of that tension adds up and becomes habitual. Often students speak with nearly closed mouths, moving their jaw as little as possible, because this is their habit. Clearly this is a jaw issue, but the tongue always compensates with the jaw is tense.
I recommend two things. First, add these massages to your warm up routine. They really target specific muscle groups, promoting blood flow and pliability. Second, set an hourly timer to stand up, stretch, unclench your jaw and stuck out your tongue. Both of these new habits can really aid to create released and free jaws and tongues (plus cut down on some stress!).