Toyota Repair: Toyota r22 1981 jerking motion, distributor shaft, toyota pickup

Question
I Have a 1981 Toyota pickup with the r22 engine in it. 2 wheel drive. It is gine under acceleration but jerks when trying toi hold a speed. e.g trying to stay at 30MPH for example. I have rebuilt the carb, and replaced the distributor shaft as well as the spark plugs and wires. Still jerking while driving. any ideas? the truck has about 200-300k miles on it. hard to tell since it has only a 5 digit odometer. LOL

Answer
Was the disteributor cap and rotor replaced or checked, if not I would recommend replacing those as well, also check the coil for any cracks and make sure the timing is adjusted to 8 degrees before TDC with the vacuum hoses disconnected from the distributor, be sure the timing advances as the engine speeds up.