TCC not engaing

according to a torque converter clutch test, the one where you cruise at 50mph and then tap the brake with your left foot to open the circuit to the tcc to disengage it, my tcc isn't engaged at 50 or 60 mph. How important is this to fix? I've learned that you lose about 3-4 mpg with a defective tcc, and that since it also cools down your atf, with-ought it the atf can be burnt and cause the trans-axle to fail.