I had this problem a month or so ago and after changing my fuel filter it went away, it's back.

It's more noticeable after the truck sits more than 4hrs.

I start up and sometimes I'll have a rough idle for a couple of seconds other times I won't.

It ceases after a second or two and the weird part is it dissipates quickly (5 seconds) as if it were water vapor but I do notice a stronger exhaust odor until it dissipates.

 

To me it seems like the injectors are leaking down when its sitting. Have you had injectors done??

I would also keep an eye on your oil level for sudden raises

 

Had 2 injectors replaced around 30k ago, cracked bodies that flooded the oil. I've been checking the oil every couple of days and no odor or volume increase, but an injector leaking down wouldn't cause that anyways, right?

I noticed it doesn't happen in the morning when it's 25-42 degrees and I let the heater cycle. I think it only happens when the heater doesn't cycle which would make sense in that the fuel doesn't burn fully due to lack of cylinder heat, but why would it just start doing it?

I noticed last night as I left the shop it definitely had strong fuel odor to the smoke and the heater didn't cycle.

 

Sounding like you have another one going out, and its hanging. You would have to have a good amount of fuel accumulate to contaminate the oil.

I agree with you on the heater cycle.

The heater should cycle for as long as the intake temp is under a certain temperature. If its not cycling in those temps you may wanna look at your relay and solenoid for the grid heater

 

The Heater grid kicks on around 59 degrees right?

It seems this occurs when it's right around 55-63 degrees and the heater grid doesn't come.

Every morning when the heater grid cycles I start it and no white smoke or rough idle.

Anyone know where the heater grid sensor is located maybe it's covered in grime effecting the temp reading?

I know the truck should start regardless of it cycling and it does, but this seems to be the only thing I can come up with.