Shortage

05 envoy Denali (not xl) 5.3l V8
Battery died two weeks ago on me after
making a stop. I jumped the car and got it
going.
Next day same issue car won’t start. Went
back to where I bought my battery and they
warranted a new battery. I take it to my
mechanic and he said my issue was there
was a strong electrical pull coming even
when my car is off. He tested everything. My
battery isn’t the issue at this point but
something is clearly pulling all the juice from
it. I had my alternator checked also and was
told it can’t be my alternator or starter. He
suggested it could be a body computer that’s
not going to sleep when my car is no longer
on. If I turn my key my radio, lights and dash
turn on so clearly my battery is charged and
good to go. But when I turn my key further it
just makes a click. It doesn’t even try to turn
over. So I’m still leaning towards my starter
being bad. But I also came to realize one of
my spark plugs is bad so I also thought
maybe it was that but was told it wasn’t that
either.
So here’s what I’ve looked into
•bad battery(not that)
•bad ignition switch
•starter
•body computer
•electrical fuses
•a bad install on my viper remote start(it was
installed before I bought my car so unsure of
when it was installed

So my question is has anyone had a similar
issue and if they did did they resolve it and or
where did they take to figure out what it is