S-10 question

I am not a certified mechanic, but in my experience with auto mechanics, I would say your transmission is slipping or is worn. Try driving the vehicle in third gear if its an automatic and see if you get the same results. If you have a five speed manual, then its your clutch, its worn. If the speed increases as you excellerate in third gear without the rpm's going crazy, then you probably have a worn overdrive or fourth gear. Take the vehicle to a transmission shop. They will be able to diagnose which gear is the problem. Hope this helps you out.