'00 Lancruiser Heater Problem: gets hot then cools down

[lee.jones]

I have a 2000 Toyota Landcruiser (46K miles) that has a interior heater problem.

The heat comes on fine (warm in about 5 minutes), and stays warm/hot for a while (maybe 15-20 minutes). But I've noticed on longer trips, after about 15 minutes it starts blowing cool air, even if I raise the temperature setting inside the car.

I know this is the opposite of what most heater problems sound like, that's why I'm puzzled?

Anyone ever experience this or have any ideas? Any suggestions would be greatly appreciated.