Your tape has probably bunched up...this could be a terminal problem for your tube....I'm sorry for your loss. :-(
I saw Alan do a neat trick with a tube by putting in strips of plastic before laminating the tube. He would then pull the plastic strips out one by one to reduce the inside diameter enough to slide the tube off. I don't know if this would work on something that long (might want to try strips of latex?) but it might be worth a shot.
I think the only way you are going to get that to remove from a mandrel that long is to use nothing but a spray mold release between the steel and the carbon and heat it considerably while it's curing so the steel expands. You'll probably still need some sort of mechanical means to pop it loose.
The guys making one-piece hiking sticks use mandrels that have a very slight taper to them and some are aluminum to take better advantage of heat expansion.