why does my 89 gmc sierra hesitate when driving or idling at low speeds?

[joe sirdar]

when driving 5 to 15 km/h the truck hesitates and almost stalls,

 

[Kiba D]

It could be a list of things. Vacuum lines could be loose, which would cause a fluctuation in rpm range while idling or it could need a simple tune up. More information would help.