1999 Suburban... What is this???
 

What are these coolant hoses doing unplugged and what am I missing to get it back in working order?

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Does the vehicle have the rear AC? could be the rear heater core pipes

Yes, it does. I'll have to check that. So, do these things have two heater cores?

I've taken it around town and I can't get the needle off cold. Almost as if the thermostat has been removed, but I haven't checked to see yet. It supposedly had a blown head gasket at some point and it's hard figuring out what's going on here...

If the gauge is not registering anything other then cold, it may not be working or its disconnected...
It will most likely run rough and rich most of the time if there is no thermostat installed, particularly when its cold out... does the oil smell like gas? if so running rich will eventually take out the catalytic converter..

Does the upper radiator hose get hot? If not, your t-stat may be stuck open or missing.

Ok, so I drove it to work this morning, maybe 10-12 minutes of city driving, heat never got anything above a degree or two above cabin temp. I got to work, checked the top radiator hose, it's not hot. The other odd this is it's also pressurized. That's a new one for me. Ideas?

The water pump probably keeps it pressurized. Sounds like what I said before. Even if the t-stat is just barely stuck open, the system will never heat up in the winter time.