my heater only works on low or med do I need a new blower?

No ... The motor has a "Resistor" for every speed. Resistors control how fast the motor will go but over a long period of time they burn out ... usually one at a time. Yours are probably inside the duct close to the motor ( Google "S 10 blower resistor location" ) it will show you where they are at, Good luck

thanks for your help

You might want to check the switch first... and if you are getting heat from the blower on low and medium speeds, I would just go with that for now. After the truck warms up, you will most likely lower the heat anyway! Let us know what you decide, ok?

I got a 1998 s10 heater will work in town when i get out on hiway it blows cold air.I cleaned heater core and new radiator new cap.

There is a box above blower motor resistor it's a relay more than likely thats what's wrong