1982 Ford F350 carburation

You may have a vacuum leak, get a can of spray Throttle body cleaner, spray the vac lines and maniflod area, when the idle changes, youve found the leak! You want the engine running and spray on the outside but do direct the stream onto the hoses, if it is a vacuum leak, the engine idle will change speed, then you have detected a leak, repair the vacuum leak and see how it runs! With 560,000 miles, internal engine wear isn't out of the question either. Is this a known good carburetor? A compression check couldn't hut!