2003 'burb front heater not blowing warm

[MASTERBrian]

Looking for things to check. Apparently the front heater isn't blowing warm air only cool. I can turn all the way too high seeing and just get cool air. The rear system works great.

I've already recalibrated the blend doors and they seem to be functioning fine. I've felt the lines going to the heater core and they both feel warm, problem is with the rear system those lines T off right near the firewall where the front core resides, so not sure if just residual heat or if it's flowing.

For what it's worth, I moved away from Dexcool years ago. The truck has auto climate control and everything in dash looks to be working fine. The truck has 220k on it.

Best part is I'm on vacation in Colorado, so heat would be nice to figure out.