Your heater seems like it does not warm as fast can that be a thermostat problem?

Yes, it could very well be your thermostat not working properly enabling the heat you seak. Or your heater core it's self could be worn out and needs replacing. But I would first pull out your thermostat and test it. If you don't know hoe to test it keep reading. You can test your thermostat by removing it from engine then placing it in boil ling water, watch it closly. the spring would have moved, if it didn't move make your water hotter. then try again. you will notice a gap started to appear in the middle of the thermostat. If it works it should open fairly wide. If it opens slightly or not at all, I suggest replacing it. Know as for your heater core, i am not to certain, but i noticed personally that when mine went, i would crank the heater and only steam or fog would come out. So i figured it was shot and replaced it problem solved. Hopefully this helps you solve or figure out your lack of heat situation. If you pinch off the top radiator hose and you get heat in the passenger compartment, it is probably a T-stat. If you feel the hose going into the heater core and feel the hose coming out of the heater core this will tell you if the heater core is plugged. They should both be fairly hot. If one is cold, it's plugged.