Check the areas around your water pump, timing cover and thermostat housing for leaks. I had the same problem for the last year. Kept smelling coolant but never saw any drips/puddles. A few days ago I finally found a puddle under the truck and I found out it was leaking just off the top passenger side of the timing cover and running down the block. The leak was small enough at first that it must have been evaporating as it ran down the block leaving almost no trace. Like you I was having to add a small amount of coolant every few weeks but couldn't find a leak anywhere. It was running behind the water pump so it was impossible to see without taking things apart.

 

Do press. test first, ck. all freeze plugs and gskts. close while on on lift.
Could also be intake manifold leak. Coolant is sucked into engine.
You can rule out head gskt. w/ exhaust probe at radiator cap neck, high hc or co readings, any shop that tests for emissions can do it.
Thats a small leak though.

 

Well, I'm pretty sure I found it. There was a leak by the water pump. It's been replaced and so far so good!

 

i still think igo u beat mines only a 2000 but its got 179,608 miles on it as of 5/3/08

HA

 

Well i have this issue aswell. All these are great ideas and im gonna have to add them to my list