I had this same issue in my 02 sport edition. The rear heater worked great, but the front would not get hot. You probably have a blocked heater core due to corrosion or a lack of regular coolant drain and flushes. Here is how I fixed mine without replacing the heater core:
1) drain coolant.
2) disconnect the inlet and outlet lines leading into the heater core. These are located at the very aft end of the engine compartment going into and out of the firewall.
3) use a compressed air gun to plow out the remaining coolant from the heater core. Simply place the pointy air gun tip in the inlet nose hole, and cover the outlet side with a towel. Blow the air in the tube. Wear goggles. This will get messy.
4) using a funnel, or tube extender of sorts, fill up the inlet heater core line with CLR (calcium/lime/rust remover). Fill it up until you see it leak out the outlet side.
5) let that sit for around 15 minutes.
6) using compressed air, blow out the heater core by pressing the air gun tip against the inlet tube. It will blow shit out of the outlet side, so have it covered with a towel. You should see a bunch of chunky stuff getting blown out. Repeat once more with CLR.
7) repeat this process with distiller water to ensure all the CLR and particles are out of the heater core.
8) reconnect all the tubes.
9) conduct a standard system flush. Ensure you have both the front and rear heaters full open on hot while you are doing this.
10) heater will now work like new.
If you need any more help, shoot me a pm. I can go out to my truck and take pictures of exactly where these hoses are and where the connect. Hope this helps!
