or you could just fill it the old fashioned way by filling it, run it to burp out some air and fill it again.
your over thinking this to much and using to many modern things. technology is biting you in the a$$.
make sure you have coolant. fill system, drive it, top system off. no more air in said system, and the small amount that would be left is not going to be enough affect your heat. drive it again, get to operating temp grab heater hose. if it's still cold its not because you have a air pocket, you have a blockage somewhere, or another reason for lack of flow to the heater core.
pull hose off both sides of heater core with motor running. make sure you have good flow from water pump which would be volume to heater core, and good volume thru the core. then blow in the return line with your mouth and verify that you have good volume back into the block. sometimes old school just works better. messier true, but better.
if your radiator wasn't leaking coolant, then what you found when you vacuumed/pressurized it wasn't affecting you. and you only have a 16lb cap, and plastic end tanks. so you might have created your own leak trying to find a leak that likely wasn't there. till you pressurized it that far past operating pressure anyways.
anyways, carry on.
tried burping it the old fashion way months ago, never worked.
after a bunch of reading on the internet i found that once you get air in the heater core you will never get it out without using the vacuum tool.
it is acting as if its an air bubble, and there is nothing to show me its not.
you'd think with all of the crap ive replaced the problem would have been fixed, but it hasnt been.
everything that has been replaced:
waterpump, thermostats, blend door actuator, upper radiator hose, both lower radiator hoses, and soon to be the radiator.
i have disconnected the heater lines and made sure the heater core was not clogged, the only thing it can be with all the parts being replaced and the heater core verified unclogged is an air bubble, with a hole in the radiator that is sucking in air there is no way to get the air out of the system under vacuum, and it will not burp. the only reason i posted on here is because everything that I have done should have given me heat.
unless of course the new waterpump is bad, but that would cause an overheat, which the truck runs at normal operating temp, which also tells me the thermostats work (even though i pulled them and tested them to verify they do in fact work)
on the bright side though i am getting really good at filling and draining the coolant
and on another note, the heat worked fine before the waterpump was changed