Be prepared to buy a master cylinder. 9 out of 10 times that's where you'll find the problem in my experience. Pull back the carpet under the pedal and look for any signs of fluid. You might not see any sign, but hey maybe it will be obvious.
Anyway, the master cylinders always seem to give up in the cold weather, the fluid leaks out into the cab and under the carpet, and then no clutch. your rig is just kinda at the right age for the problem too. They are only good for about 1,000,000 pushes.