Fixed coolant leak at water pump gasket months ago and I check the level all the time. The tempature suddenly dropped and now the level was real low. Could cold weather cause it to drop in the tank? I'm positive there isn't a leak. It has been fine for months other than level bouncing back and forth a couple of times.

 

Yes, colder temps can "shrink" the water to an extent... if its only a small amount, that is what I would suspect...
You could top it off while its cold to a known level point, and see if it drops from there. If it does then you may have a leak or its being consumed... if it stays the same or goes up, well then you'll know, no leak.

 

My coolant has been doing a disappearing act for over a year now. I pressure checked the system and it held pretty good. I can't find any signs of a leak other than the coolant level, so I just add a little to the reservoir every month or so. I know there was a service bulletin for porous cracks on some of the heads on this trucks but I really never looked into it any further. I figure I'll just keep adding coolant until something finally breaks or I trade the truck in and its the dealers problem to find.