You ever find out what went wrong here? Sounds like I am in the same boat amigo.
You can do some quick troubleshooting.
1st thing. Is the engine actually heating up? If you believe the crappy factory temp gauge, is the engine actually warming enough to get heat? Remember this is a diesel, it is not going to warm hardly at all unless you get out on the road and use the engine.
2nd. You can do some quick troubleshooting. If you think the engine is warmed up, when it's running lift the hood and grab the heater hoses. If the engine is up to operating temp (about 190F) you will quickly let go of the hoses, they will be hot. If the engine is fully warm, but the heater hoses are not very hot, suspect no flow through the heater core because of a clog.
3rd Another way to verify the engine is fully warmed up is to grab the upper radiator hose. If it's cool to the touch, the thermostat has not opened yet. When you start the engine cold and it is starting to warm up, if the upper hose is warm, the thermostat is stuck open.