I own a 2000 s10 ext 4.3 manuel truck. The problem i am having with it is that the revs are sticking between 1000 and 2000 rpm. When the truck is is at idle it runs fine and normal but i set of driving and and the revs stick i go to change gear and the revs dont drop when you put your foot on the clutch to change. so i can be driving down the road and not need to use the accelerator to drive it just runs on its own, It then will drop down on its own accord and be fine for a bit and then it wil start doing it again,

Please help me if any has any clues to what is going on

Thanks