[vash]

there is a valve that lets the heated coolant move into the heater core. on my 96 chevy, i sometimes needed to beat that thing to get the water moving.

what were the truck's operating temps looking like? "long time to get warm..." you talking about the truck temps or the heater temps?

my money is on that valve.

FYI, is your coolant red? my dealership told me that coolant sometimes gelled up, and would clog the heater core. my truck would sometimes sound like a coffee maker. it would gurgle behind the dash, or sound like a cascading fountain. i flushed my heater core and it heated up much faster, and the sounds were diminished.