2004 2500 6.0 Silverado ac blows HOT on alternate sides of vehicle while in Auto A/C mode.

Douglass, Your A/C may have lost it's programming, blend door actuator could be faulty or A/C could be low on refrigerant. You may have to take in and have a good Tech. diagnose and estimate repair.
Check the attached links,instruction and guides, Good luck
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Dual climate controls drivers side hot passengers side cold have 2004...
hot on driver side
Drivers side vents will blow hot air while is turned on but passenger side...

A vent flap actuator probably needs to be replaced. It's what moves your vent flaps from heat to A/C or to plain "vent air" when you change settings.

The discussion in the link includes vent flap actuators. Unfortunately, they also include the infamous no low speed fan problem too.

Cannot get any air from dash vents while defrost and floor vents work fine...

Your particular actuator will be a different one than they found.
They're all a absolute pain to get at because they can be well buried in the dash. I would start looking under the dash on the passenger side, that's where most of the air control is.