Where are you? What temp are you driving in? Was the truck parked outside? The reason I am asking is the linkage might be frozen up.

By the sounds of it, if you can't get any gears when it is off, then I would also think that something in there is locked up, or the linkage is locked up causing the clutch and thow-out bearing to lock up.

It is hard to say with-out getting in there and looking at it. Try thawing it out if you can if it is frozen. If it still won't release, then it is pull apart time.

You might also want to post this in the tranny forum as you might get more help there. Good luck.