I'd start by checking the linkage from the clutch pedal to the clutch fork. If all that is ok you will need to pull the transmission. You will want to take the floor plate out in the cab and that will give you plenty of access. The shop manual has good instructions to take things apart, the torque tube is not as hard as it seems in the manual. Just take your time. The worst is the bolts for the u-joint. Make sure to use a good fitting wrench so you don't round the heads on those bolts.
