It sounds like your thermostat may be stuck open. I have the same issue with my 2001 Chevy Van, and it seems to take forever to get warm, and my heater is real slow to get going, but it does work eventually.
If I let it sit and idle for a while (like in the driveway or when sitting in a drive-through), then the gauge will go up to around 200 degrees, because no air is flowing through the radiator. Then the air temperature coming out of the heater vents gets up to about 120 degrees (I have measured it).
If you want the instructions on how to change the thermostat, please let me know. But what I would do first is check the heater hoses (going to and coming from the heater core) and make sure they are both HOT to the touch once the engine is warmed up. If both sides are not hot, you could have a flow problem through the core.
I would also make sure that the cooling system is absolutely FULL. Sometimes when it is a little low, there is limited flow of coolant through the heater core, and you will not get much (if any) heat transfer from the core. You can check the level in the radiator when the engine is cold. It should be right up to the top of the radiator neck. If not, start the engine and watch the level as the vehicle warms up. You should see it drop when the thermostat opens, or it will drop and you will see it flow if the thermostat is stuck open. Just top it up to FULL, once you see it flow, and put the cap back on. Then test the heater again, and see if it is any better.
Please let me know what you find and if you want those instructions.
Take Care, Greg A.