any reason?

 

Are you serious?
If you have a problem with your vehicle you are going to have to supply enough information for people to help you. Information such as what year the truck is, what the exact symptoms are and when they appear (more than just "4.3l jerks when cruising at low rpms on fwy"), what, if any, things you might have done to try to correct the situation. Diagnosing and correcting a vehicle's troubles via long distance is difficult enough under the right conditions.

 

Yes, more information is definitely necessary.

Is it a directional problem like the steering taking you to the left/right? Or is it an engine issue where it is bucking/stalling? That is just the start of the questions. The more detailed you can be with your description of the problem you are experiencing, the more detailed we can be in the diagnosis. For us to just make guesses wastes everyone's time.

 

Okkkk the 4.3l hasnt changed much in design....
I have a chevy s10 99' My engine hessitates while cruising 70mph. I have an automatic, so at the lowest rpm, i get this hessitation, kinda like back fire. Seems to only happen when its humid outside. It will happens when the engine is cold and fully warm. So pretty much all the time.

 

Well that narrows it down a bit better. Sounds like an ignition (spark) issue since you have stated that humidity affects it.

 

how would i fix that problem?

 

Diagnose it... This forum has a wealth of information. Sorry if I am short on the direction I give, but there are MANY people requesting help. To spell it out for everyone would be a full time job. The search function works surprisingly well. You should be able to find many threads on "ignition", "spark", "humidity", etc keywords that should point you towards the proper diagnostic steps you need to take.

If you have not done a complete tune up (plugs, wires, cap, & rotor), now would be a good time to do so to rule these items out.