Okay I will start with saying my truck has 190k. It is a 1995 F150 with a 302 and a 4R70W transmission. Now on to the problem. If I am driving at 60mph or higher for more than 30 minutes the tcc will unlock and I have to slow down to about 45mph and then accelerate enough to get it to downshift without going into passing gear or even enough to go into passing gear, but once it downshifts it will then allow the tcc to lock back in for another 25 to 30 minutes. The odd part is if I stay at 55 mph it will stay locked the whole trip. I am perfectly fine with driving at 55mph since I am getting between 19 and 20 mpg before I installed the tonneau cover last night. I am hoping to increase the mpg with the tonneau cover, but I still want to fix the tcc problem before it gets worse or damages the transmission.