If its not a hydrolic clutch like mine follow the linkages, for me the linkage last before the clutch fork and an adjusting bolt on it to make the rod move forward and back.
To me it seems like your clutch isnt disengaging from the flywheel. this would be evident if you put it in reverse with the clutch pedal pressed in and turn the truck over.
If the truck moves your not disengaged enough. and from my readings and experience these are you options.
1.
clutch linkage adjustmest, should be simple and can be done by sliding under the truck. (if a non hydrolic clutch, if it is then im sure its somewhat similar)
2.
your clutch is frozen to your flywheel from sitting for to long
3.
and this has just been my freak misshape which was one of my flywheel bolts came out and was not allowing me to disengage the clutch. This also could occur if one of the clutch pressure springs broke or has come loose.

any more info about the issue would be of help! and ill do my best to give you tips from my experience with clutch issues, Ive done a lot of researching on the subject.