First post, did a search but didn't find anything similar.
I have a 2000 Buick Regal GS. Has a dual automatic climate control. The heater works fine when driving around town. However when I go out on the highway it stops working after about 20 or 30 minutes of highway driving. The fan stops blowing and no heat comes out. After slowing down to city speeds, the heater starts working again. Strange.
It is a bit of a problem since the outdoor temps have been very low this winter. I took in to the dealer and they have no idea what is wrong. Any ideas to that might help?