I ave a 1975 Dodge Sportsmen RV, V8, 318 engine. She starts up with no problem even in cold weather. The choke does not shut once warmed up, is always open. Once in gear she stalls out. Once on the high way She drives smooth 30 and above mph, but again at low speed 20 or below she tries to stall or does at time stall out. What could be the problem
The choke should close when cold, not open, and open when the engine is warmed up, not close.
I’d suggest you take this to an old time mechanic who understands carburetors. From the sound of it, the choke and its associated linkage (high idle cam & linkage) may in fact not be working. The bimetallic springs that drive these things get old and tired over the years. But considering the car’s age, there could also be other issues, like a sinking float in the float bowl, a gummed up/improperly functioning needle valve (that allows the float bowl to stay full without overpressurizing), and/or other carburetor issues.
If you are able you can still order rebuild kits on the internet or a complete carburetor. Some of the major parts chains might have what you need.
Does this 318 have the 2 or 4 barrel carburetor on it?
Are you sure the idle speed screw is correctly adjusted? It could be that simple.
Is a tune-up due? If due that should be taken care of. But specifically to your poor running at low speeds, if a tune-up is not needed it sounds like a vacuum leak and the carburetor to intake gasket was a common failure on that engine and a leaking egr valve also. As above, I believe that your choke is operating properly.
Look at the wires in the distributor and if they are frayed change out the parts.This stalling is usually ignition related and sometimes just plug wires.