My truck is 2004 1500 5.3 liter automatic tranny 140000 miles. 

So there's been no heat in vehicle for awhile and the truck also sat for 1 year without being started, not sure if there was any antifreeze in system.  So I changed out the heater core and new water pump, a thermostat, some of the hoses, flushed system before hooking up new heater core.  Seems like I'm having issues getting all air out of system.  When I think I do have all air out I will drive around 2 miles and it will start running hot again and when it does get hot it feels like the rear brakes are being applied..  I've bleed the air out several times there is no sign of water in oil.  I haven't checked cylinder head pressure yet there are no noticible water leaks .  I did flush radiator.