Help! Vortec 6.0 Pushing coolant out of resivoir

Help, I have a Chevy express cutaway Van with approx 6,000 Miles. It has a Vortec 6 Liter and 4.10 rear end. It has been leaking coolant since day 1. The dealer replaced the water pump at about 3000 miles to fix a coolant smell and leak. The smell dissapeard but the truck still leaked. I traced it back to the overflow tube on the coolant resivoir. Took it back in the next week they said the radiator cap was bad. Put on a new one still have the same problem. It will push fluid out of the resivior until the level reaches the cold full line and then stop. The fluid dosn't move from that spot either when the truck is hot or cold. Also, as the fluid drops the catalitic converter smell gets awful...I mean dead skunk awful. The lower the level the worse the smell and mileage drops. The dealer is stumped I'm stumped any suggestions?? Anyone else had a simmilar problem? Thanks

Head Gasket Leak????

This is the third try for the dealer to fix the same problem. I am not sure about your state but in mine if the dealer can not fix the problem you are having in three trys it falls under the lemon law. Contact a lawyer.