I third the exhaust leak on the knocking sound.. mine at the manifold always sound worse on a cold start. I know some oils cause a knocking sound for me on cold days with cold startups.. but my motor has twice as many miles as yours..
You also just might be hearing some of the water that accumulates when cold being burned off by the motor. Does your truck blow a ton of steam out of the exhaust when you first start up in the mornings?
Scary enough, that's all coming from the oil and it's perfectly normal. If you don't see it, make sure your PCV valve hasn't seized!

As for the low idle and dying, could be anything. Is defrost on with the heater? that will also turn on your AC compressor which puts a bigger load on the engine and will drop the idle. If it's a bit out of time, has a dirty IAC or something along those lines it could definitely push it to the point where it dies, especially on cold mornings.
It might also be weak fuel pressure, slow injectors, clogged / frozen PCV valve, all of which are common on these trucks in the cold if things haven't been changes.

did you check codes on it? Do that first.. it might point you to exactly what's causing it. TPS or IAC or .. well, there's plenty of sensors that could cause this. If your EGR valve is stuck open for example? just run codes