Strange Electrical System Issues
 

So, today my battery light comes on. I knew I was about due for a new battery, so I just planned to go pick one up later.
The last few weeks after the truck sat for a couple days without driving I'd get an HDC Hill Descent fault when starting it up, then it would clear and go away. So I figured my battery was starting to go.
Before I get home today, other lights start dinging on my dashboard, and multiple other faults start going off -- yet it keeps driving fine, suspension didn't lower or anything.
Slowly, I start losing power, and notice it's lagging.
I'm still driving, but faults are still going haywire... I turn off lights, radio, heater, and it seems to juice up the battery some and faults subside a bit.
Slowly it keeps draining and I keep getting faults.
I'm headed straight to the AutoZone to get a new Optima Yellow Top battery.
I limp my way there and make it into the parking lot.
Replace the battery with the Optima.
Starts right up and things seem fine for a few minutes idling.
Then my battery light pings again.
Then I seem to detect some kind of humming noise coming from the engine compartment... I've still got the hood up... and I can smell some kind of electrical ish burning smell...
Things start to go haywire again on the dash one by one, loads of different faults, transmission fault, suspension fault.... then everything slowly just drains down to nothing -- and then it's completely dead and won't even turn over. I can't even lock the doors in the end there's not enough juice.
So -- I bought a new alternator -- suspecting that's what's wrong, and that it just drained my battery quickly since it was a brand new battery that just may not have had a decent charge on it... and I've got it scheduled to tow into the shop in the morning.
What do you guys think? Am I diagnosing this correctly? I'd like to know what I'm getting into if I can.
Thanks in advance.

I'd say alternatives well. I remember mine howling on its way out as well.

For what it's worth I had no issues running a gold level battery from Advance Auto for years. They do stand by the replacement warranty as well. Mine died just before the 3 years were up and they grabbed one off the shelf at no cost and reset the warranty to day 1

@russlowe check your ground strap too, especially at the body connection. Known for getting loose or corroding causing the Christmas tree. Given the smell and sound though most likely an alternator