Missing at all speeds

I own a 1986 Dodge Ram 5.9 L, 4bbl, automatic 2 wheel drive w/ air and the truck misses at all speeds. Seems like it misses on only one cylinder. I changed the plugs, wires, distributer cap and rotor. Also changed the oil and filter. Engine was rebuilt 35,000 miles ago. Distributer was rebuilt and so was the carburator. I am at wits end so can someone help me?

You’ve gone and changed everything that I would have done to start with. I assume the timing is set right and the distributor was indexed right?

Is that cylinder getting fuel? Meaning is the intake manifold good to that cylinder? Have you opened the valve cover to make sure that cylinder’s valves are ok? I don’t know if that’s overhead cam, but probably not so are the lifter rods in ok shape or it that keeping the valve from running?

Have to checked that cylinder is getting good spark so you can eliminate electrical as a source and maybe fuel instead?

It’s only questions I have, but maybe they’ll lead you to an answer.

In a shop setting, the first thing I would do is run a compression check.
It’s entirely possible that the rebuilt engine could have a problem.

A vacuum gauge could also be connected to the intake. If there is a problematic cylinder then it should show up on a vacuum reading.

Pull the plug wires off one at a time and see if the engine runs any worse. When you find one that doesn’t change the engine’s performance you’ve found the cylinder that has the problem. Then you can find out why: bad plug, wire, valve etc.