I glanced over the thread. did bothe hoses use to get hot and now after the new tstat only one hose works. it sounds to me like a clogged or bad heater core and posible and isue with the heater control valve. the valve is usually in line with the heater hose but in olde trucks might be somewhere else. heater cores on your truck are an cheap easy fix. you could get a 5/8 connector and pull the heater hose of the firewall and connect them. if they all get hot it is most likely the heater core. if not you might have a clogged hose or look for that heater control valve

 

your core could be clogged and backflushing might clear it up

 

I have a good update. I pulled the heater core and flushed som nasty sh$# out of it ,put it back in and now it works fine. Thanx to all on great advice with this issue.

 

your welcome and that is great that you got heat!!!!!!!