Radiator Balance/Boiler short cycling issue

One pipe steam, additive pressuretrol.  HELP.

Brief History:  System has worked pretty well for years, after some work to balance it.  This despite the fact that the Main vents were undersized (after two different plumbers told me nothing else could be done to replace the ancient ones because the thread size was too small for newer ones.  I wondered then--I'm smarter now--and ticked.)  Thinking back, probably not working as well the past few years--but not enough that we really noticed it.

This winter: 

First, no heat at all on single digit day--despite boiler running non-stop.  Had plumber in.  Said not getting enough gas--check with PSE&G before he replaces boiler gas valve.  PSE&G fixes it--condensation in the outside line had frozen.  Said pressure good--probably better than before.  

Second,  next really cold snap, pretty similar symptoms.  Called PSE&G first.  Pressure checked out ok.  Saw crud underneath and said boiler cracked--but it has not been losing water.  Plumber comes for second opinion--no crack at bottom, tests for crack at top--all good.   Checks pressure controls--badly clogged pigtail.  He replaces it.  Things much better, but radiators in stack (1st, 2nd, attic) farthest from boiler not heating.  

Third, I do some research--maybe bad main vent.  I take it for replacement and explain it's a hack, and I really would rather the right size--they give me Gorton #1 and parts to downsize.  (Other main was same, I replaced it too with right size.)  Those 3 radiators still cold.  So I research pressuretrols.  Cut in was set at 2.5, inside dial at 2.  (Additive)  I lower cut-in to 0.5 and dial to 1.  Better.  Downstairs and most upstairs rooms are lovely.  First floor rad gets heat--after an hour or more.  2nd floor takes 3-4.  Nothing in the attic.  This is in the morning.  Boiler seems to be running constantly till it gets up to temp--at least every time I check.  Later in day or evening I am less clear on--though attic rad got a teeny bit of heat last night before system went to night temp.

SO:  I am thinking I need to get bigger vents on those radiators, but I want to know if I can just change them and leave the rest alone.   Also wondering if I should have a #2 on the long main--though it does not have any risers off of it--and as near as I can tell the far radiators must come off a short end riser(s) which then goes over.  And/or could something else be involved in the short cycling.

I can do pictures as needed.

For help did you try these guys? https://forum.heatinghelp.com/categories/strictly-steam

I would change the vent on the last radiator in the stack to a large one first, and if that helps some change the next one down as well.  I think you are on the right track trying to get air out of the system as quickly as possible. 

Thanks--that makes some sense.  And thanks rwh, I have now posted there as well.

Any chance you've replaced the thermostat lately? They have settings for forced air furnaces vs. steam boilers. Mine was set incorrectly and my steam system was having all kinds of issues until I changed the setting.

Same thermostat--but that's good to know.