You probably have it in two gears at once. I would fiddle with the levers for a while and it might just come out of one. There is an interlock on the transmission side cover that is supposed to prevent things like this. It may have been overcome, allowing the gears to jam and is now preventing them from going back. You may have to remove the side cover and manually manipulate the gears. Be careful when you do this as the shift forks want to fall out of the cover if you hold it wrong.
Uhh, I suppose this not not a good time to make an offer on that great looking truck, is it?
