If your exhaust does not smell sweet then it is likely not a head gasket problem. I have been chasing a coolant leak on my truck for quite some time now and I have finally determined it is the gasket for the oil cooler at the truck. I still have yet to get the first drop on the ground because the leak is slow enough and the engine is hot enough to evaporate what does leak, just enough to give you a whiff of a smell and only occasionally then and the dropping levels of coolant in the system.
As for the smoke since I am going to guess that your programming is not new it is not a real likely suspect the more probable answer is that something, likely injectors, wore out and you're getting poor atomization which would cause incomplete combustion resulting in a greyish (black) haze. I've seen problems similar that were an injector nozzle. You should be able to determine the source of the problem with a cylinder contribution test
