I hear about that plug on the mixture, I have 3 carbs and I have yet to see that plug.  The idle was bad so I tried to adjust the idle screw didn't work, so I tried the mixture and I F'd it up worse.  Then I took it to my mechanic who adjusted the thing properly.  Now it is still running too rich which 3 mechanics including a carb shop said means I need an overhaul.  I priced an overhaul at $392 dollars so I can get a weber cheaper but I want to be sure it will not put out rich readings too otherwise id rather just rebuild this one.  

if you don't want to over haul the carb yourself and the best price you can find is 392 then i would definatley vote for the weber.

on the other hand if something other is wrong with your carb and the mechanic tried to fix it by adjusting the idle mixture screw then you might be chasing your tail.  did you or the mechanic write down exactley how many turns the stock setting was before turning it?  if so put it back to where the factory set it and start testing the carb.  i find the chiltons manuel on these trucks to be very helpful with this.  the tests are very simple, they involve stuff like pulling a vacum line and looking for a squirt of feul in the barrels or pulling a vacum manuely to make it die, among other things.  give it a try.  if anything you will come out of this knowing a lot about your carb.

i would check that AAP valve first.  usually if it's bad there will be gas in the vac line.  pull the vac line after it has been running and see if there is fuel in it.  

or if you don't want to mess with it buy the weber and bolt it on.  i definatley like the webers better.  they have smooth acceleration and are prety reliable.  

did you know that the stock 22r carb has more CFM than the 33b weber?

good luck
mike