What is jumping time and why does it happen and how do you fix it 95 4.3l vortec 4wd

Jump timing is when the timing chain becomes loose and may jump a couple of teeth from the gear. I doubt this is your problem. I have never had any vehicle jump a tooth. Usually they just break. Take off your distributor cap. Have someone hit the key while you watch the rotor. Did it turn when the engine turned? If so, your timing chain is not broken. If not turning, the timing chain is broke. Check your air intake hose that attaches to the throttle body. Did it come off or is there a large crack in it? I had one split and my car did the same thing. Just sucked air and died. The hose had split causing too much air flow. The car would instantly die out. Also check all your vacuum lines. Make sure all hoses are good. If all looks good, your fuel pump may have died also. The car will not sputter if the timing chain lets go. If you are getting fuel, then check for spark. Your coil may have failed also.

That is when the timeing chain or belts gets worn and it allowes the crank get out of time with the cam. It is time to replace the timing gears and chain