Honnelee Gibbs

I need some advice ...my BFS truck 2004 Chevy Silverado 1500 has dual heaters ....the passengers side pushes heat (like it should) but the drivers side is coming out cold . we took it to a garage they said the actuator is working , but it's more than likely the door is not opening to let hot air through .I've researched the process and how long it should take to fix this ....I see a couple hours because the whole dash needs to be taken apart ...the garage states the flavor book says 6 hours to dismantle dash and replace door.....I need advice please....is this realistic 6 hours of labor ????? Of not I don't want to pay almost $400 in labor for this unexpected problem...we just bought the truck 3 weeks ago ....of course the seller stated no issues ....now I'm looking at a huge bill to have heat on both sides.....any help would be awesome ...thanks everyone