Truck stuck in gear for a moment?

I have a 94 chevy s10 its the v6 with vortec. I bought it 3 days ago and feel im ripped off. I took it on the freeway and floored it to play with the vortec and the rpms just went way up into red and then the rpm and mph gauges started going up and down all crazy and the service engine soon light was blinking this lasted about 20 seconds and i of course got off the freeway. but i had taken it about 30 miles and back three times on the freeway didnt have problems. It drives fine in town and havent tried the freeway sinse then. could this be electrical or maybe tranny issues? it is automatic. It's just the gauges freaking out is what makes me think its not tranny related.