5 min seems about right for the v6. the 318 warms up alot quicker.

Make sure the new thermostat is actually working. Simple way to do this is to take is and stick it in a pot of water on the stove with a thermometer in it. When the thermometer reaches 195 degrees F, the thermostat should be in the open position. If it's not, get another one and do the same test till you get one that works. It's old school and a pain I know, but a proven method.

BTW my 5.2 gives crap for heat too. I've replaced everything except the heater core. It's on order.

Yeah...about that....hehe. Mine's almost ten mins. before I get any warmth from the vents.