Transmission stuck in fail safe mode

Has anyone heard of this problem? Four days ago my B4000 4x4 splipped into transmission fail safe mode. I took it to the dealer and they can't find the short that keeps blowing the #13 fuse (chicken or egg situation) is the tranny blowing the fuse or a system electrical short setting the tranny to fail safe mode?
Poor acceleration, stay inwhat seems to be 3rd gear forces me to take take off by manually shifting my automatic tansmission to 2nd and shifting back to normal drive at 30mph. I've been driving the truck to work on the freeway at 70 mph. Is this damaging my tranny?