it was the damn plenum gasket.i had the dealer do it.it idles fine now but i kept hearing a running water sound behind the dash like a gurgling noise and the heater blows cold even though the truck is warmed up.

 

gurgling sound could be air trapped in heater core..located just behind dash on passenger side. I was told I have the same issue, but need the knowhow to bleed the air out..any help?

 

park with the front end elevated. remove radiator cap (don't get burned), and let it idle for a good while with thermostat open. rev it up a little to get good water pump flow. fill overflow tank to max, replace cap, that'll likely stop it. if not drive it a couple more days and it'll go away.