I don't think that the vacuum should move rhythmically. Do you have a shop manual?
If your timing is too far advanced, pulling the choke might straighten things out.
What you might want to do, is put in clean plugs, set the timing as per the manual, and the idle, etc., don't drive with the choke on. Drive the truck around for 30 minutes, so its warmed up. Now, find a gentle hill, where you can accelerate at full throttle, in top gear, from about 25 mph. Now after running at WOT for a few minutes, push in the clutch, turn off the key, coast to a stop. Do not let the truck come back to idle, just shut it off. Pull out the plugs, and stick them into a piece of cardboard, labeled as to which cylinder they came from.
Now, put in your spare plugs, and drive home.
Now that you are at home, you can take your time, and look at each of the plugs. This will tell you whether you are lean, rich, etc.
Just my thoughts. Pick a hill where the above can be done safely.
