OK - OE still R-12 never changed. You said "black died" about the compressor which IDK what you really meant - compressor or clutch froze or what yet. Black Death is a term used is mandatory to flush out everything flushable and toss anything with desiccant.
Re-read you added what my book calls for a 100% oil charge of 7oz when ready but left the accumulator on which may have had ounces still in it you can't get out and measure without drilling a hole it them, heat them up and see what comes out.
Now, no telling how much oil is in it or exactly how it failed if told you could leave the accumulator by a pro if a pro? Two type of accumulators used only difference is one is threaded fittings and the other spring lock type like this.....
If threaded items are not steel to steel an alloy will be frozen up like welded usually and bust the evaporator.
IDK - Trucks seem to put in what was ordered when new with whatever HD options changes things.
I still just can't know what type pump or gauges you are using that you can't hold a full vacuum but holds at 24? Why on earth did you leave a pump running any longer than the max vacuum it would pull and lock off system from pump - a slow one would only take 15 minutes if that long. All night you are wasting the pump. Empty is empty so running it forever does nothing more. There's no water left at 24 Hg. really unless it was obnoxiously cold out which it isn't. I don't have the chart handy but water boils at some insane low temp under vacuum, then as vapor is removed.
OK - here's a spot that could be trouble. Your pump can do a full vacuum on gauges/manifold set so we know it works. The low side fitting on accumulator may not be so perfect and not seal right in some way. Odd that it would hold and stop at 24? I can't explain that?
You could just vacuum from the high side, plug low side hose and read the vacuum. As said, zero is zero - whole system is zero (29,92 Hg.) is it for sea level minor adjustments for most by altitude. About 1 Hg. less seen per 1,000 ft. of elevation. I don't work in that so can't expound. I'm at 232 which is insignificant as things go for this for my own anything.
I'm at somewhat of a loss with both the pressure testing and now can't hold the full vacuum - refresh that you are only sealing out about 14.7 PSI of pressure at max vacuum not holding IN the operating pressures it mush be able to but is a clue if it holds a vacuum that it's likely to hold pressure - with exceptions to anything.
So if the "spring lock" connectors you need the tools to release those.........
Cheap but a must have if that type.
O tube must go and flush this out and start over. Perhaps see if compressor when turned will spit out any junk now or flush some mineral thru again and see if junk or what is in it? Run thru a coffee filter or something.
Other: Ask places like Autozone if you can rent (free for deposit) gauges and a pump as there's something not right about all that.
You do need an adaptor for high side OR if your gauges are for R-12 get the adaptors for 134a and the port adaptor for just the high side to temporarily leave on for looking, service or whatever. The adaptor to fit R-12 hoses can easily be the leak if left on.
There's just so much that isn't behaving for you I don't understand? I would be using a second set of gauges or another pump - anything to rule out why it's doing this to you doesn't make sense yet,