How does your heater work?

[95K1500]

My dad has a 2000 silverado 1500 with the v6 and he is allways complaning about how his heater is not very good. I have a 95 v8 and the heater in it will run you out of the truck its so hot. The heater in the 2000 sometimes will not even defrost the winshield.
Is there somthing wrong with his heat or does this generation of trucks not have as good of heaters than the older ones?
We did replace the thermostat and anti freeze last year and that made no difference.