My heaters as poo too. I used to have a 2.0ltr twin cam 8v engine in my old sierra and the heaters were mint. The heaters in my cossie are poo. If i just leave the engine idling the heaters get really gmt but as soon as i drive it they just get warm. Its that time of year where i need my heaters i was thinking about putting a piece of card board in front of the radiator like in the mk3 days lol.