Shifting sky high

Hey, im a new guy and i've got a problem... kink of. I got passed down a little chevy spectrum, isuzu i-mark or whatever you want to call it. I want to sell it becouse i have no use for it and am not fond at all of cars anyways. But its got a problem i was jumping the old plow truck becouse it was handy, and stupid me put the negative on the positive termanal for a secound. Now it shifts at a very high rpm but it does shift through all gears. Its an automatic 3 speed im guesing electrical. Where should i start looking what could it be?? Thanks alot